Meaningful Background Event

When some critical event is due to happen, it usually happens all of a sudden and this moment is accompanied by camera focusing and music effects. But think of a scene where we can see the event going on for some time. No Ominous Latin Chanting, no triumphant music, just some sort of silent background process, which an attentive viewer can notice some seconds earlier than his attention will be drawn to it forcefully by some means.

The similar Funny Background Event is used less for plot development and more for comedy.

See also Dramatic Irony.

Anime and Manga
"Mr. Experiment: Thanks for tuning in, all you curious kiddos! With the body of an adult and the heart of a child, lovely whiskers and gentlemanly ways, I'm Mr. Experiment! [...] In this corner let's try to solve mysteries found in your everyday lives!"
 * In Paprika, it's entirely possible to miss in the background of a mostly still shot of Dr. Chiba and Shima.
 * Before the sudden and gruesome death of in Magical Girl Lyrical Nanoha StrikerS, we actually see the killer moving closer to the victim in the background with each shot of the room they're in. But since, it's quite easy for the audience's mind to ignore it the first time around.
 * In the Suzumiya Haruhi anime, during the episode "Live Alive", we can see Haruhi and Yuki with their musical instruments walking through the background, foreshadowing their unexpected involvement in the ENOZ concert. Earlier on, the two uninjured ENOZ members can briefly be seen running past in the foreground while the main characters are talking. And, even earlier on, all four members of ENOZ can be seen arguing with the student council representative in the background, as shown up close in the flashback later in the episode.
 * In Fullmetal Alchemist Brotherhood, while Al, Heinkel, Marcoh and Yoki's car breaks down in Central, you can see walking in the background.
 * Code Geass has a rather divisive example. The death and return of was seen as an Ass Pull by some segments of the fandom. Others, however, pointed out some of these in the death episode, particularly . Additionally,
 * In the background of episode 6 of Persona 4: The Animation, Nanako leaves a television show playing while the conversation with Yu and Dojima is going on. The words are fully intelligible, and it's very obviously reminiscent of  much later on.

Comic Books

 * There's a scene in #6 of the original Elf Quest series where Cutter is telling the Wolfriders he's made an important decision. This goes on over three panels, and in the background of these panels his lifemate Leetah and his best friend Skywise are apparently conspiring literally behind his back.
 * In Marvel Zombies, the Wasp surprises people on two separate occasions. Both times, you can see her in the background the panel before she pops up.
 * In one issue of Legion of Super-Heroes, Legion leader Cosmic Boy is having a talk with the President of the United Planets over a viewscreen. In the panel backgrounds, you might not even notice an electronic pad on the President's desk quietly floating up and away—the only visible sign that Legionnaire Invisible Kid is making off with some damning information while Cosmic Boy provides a distraction.
 * The strange-looking redheaded man carrying the "End is Nigh" sign in Watchmen.
 * In the beginning of the Half a Life arc of Gotham Central, almost a full issue before the Reveal, Brian Selker (Private Detective) is following Renee Montoya to a restaurant called "Maloney's", taking intrusive pictures for a lawsuit that is about to be leveled against her. Being a long-distance shot in a comic book, with hand-drawn lettering instead of typed, there is not a lot of detail to be made out about the restaurant, and the name almost seems to be drawn as an afterthought: Maloney's Bar & Girl. It is not a typo, it is a revelation, and if you missed it you need to wait until the end of the issue to get the full story.
 * In Transformers: All Hail Megatron while the Decepticons are smashing up everything in New York, the reader might notice that in the background Thundercracker dosen't look particularly happy about what's going on..

Fan Works

 * In the Firefly fanfic Forward, during the "Charity" episode, there are several minor scenes involving Zoe walking around with a child from the village named Katie, whose parents were killed in a raid, and whom Zoe became attached to out of a sense of maternal protectiveness.
 * Rare literary example: In With Strings Attached, the four and the Hunter find themselves on a ledge overlooking a 500-foot-wide canyon that they have to get across. Paul and John get into an inane argument about whether or not Paul should jump across and thus break the ledge, while behind them, the Hunter calmly sets up a series of magic stepping squares across the canyon.

Film
"Nigel: (cheerfully) Toddling."
 * In Aliens, we see a facehugger drop from the ceiling moments before it attacks Ripley.
 * In Signs we first see the shadowy figure of an alien on the roof while Mel Gibson assures his daughter nothing's there; however you only notice it's there when it moves at the end of the scene.
 * In The Matrix Reloaded, when Neo flies to rescue Morpheus and The Keymaker from an explosion, we can see Neo coming from some distance away, before he grabs the two and corresponding music plays.
 * In the film The Mist, the man standing on the watch handles his evening meal; the camera shows him and the view out of window which he must guard. We can see a bug silently flying from afar seconds before it actually smashes in the glass and sets everyone (including the viewers) on alert, as we realize that, instead of a normal-sized bug a few inches away, it's a bug the size of a hubcap halfway across the parking lot.
 * In the American Pulse, the main characters ride in a car and are busy talking. The viewer follows their dialogue and is quite startled when another car smashes into the characters' one, although we could see the second car coming for a while.
 * This happens in Jeepers Creepers as well, only instead of the truck smashing into their car, it drives up close and blares its horn before proceeding to drive them off the road.
 * Also used when a truck approaches from Trish's blind side as she's watching the road . To say nothing of what the audience gets a glimpse of, when Darry stops to tie his shoe with the flashlight under his arm, so its beam.
 * And in The Forgotten, the same thing was done when Telly and Ash are driving and you can see A Friendly Man's car rapidly approaching them from the side.
 * In Peter Jackson's The Lord of the Rings: Return Of The King Shelob approaches Frodo silently, with no music. The entire scene is played for as much "Look behind you!" dramatic irony as possible.
 * In Fellowship of the Ring you see the giant eagle behind Saruman right before Gandalf jumps from the tower of Orthanc.
 * In Finding Nemo, the whale approaches Marlin and Dory slowly from behind before it swallows them whole.
 * In Death Becomes Her, after Ernest has pushed Madeline off the stairs and is on the phone, Madeline can be seen standing up in the background. As she approaches the foreground, the audiences slowly realizes that Madeline's head is on backwards.
 * In Men in Black, Agent J and Agent K are sitting, contemplating their navels and covered in alien goo, when in the background out of focus something stirs... and then lunges for J! Only to be obliterated by a chick with a really big gun.
 * At the beginning of the movie, we see a ramshackle house with a starry sky above, and hear a husband and wife fighting. Unless you know what you're looking for, by the time you notice that one of the stars is moving and getting brighter, it's already been moving for some time.
 * Pretty much all of Cloverfield, a film that does not stop to make sure you know what's going on.
 * Particularly
 * In the airport at the beginning of Red Eye, Cillian Murphy's creepy villain is first introduced this way, standing quietly in line behind Rachel MacAdams for a good amount of time.
 * The Japanese horror film Chakushin Ari (remade as One Missed Call) had an example of this. The main girl and her love interest are in the ghost child's former apartment, in broad daylight, searching for clues about the child's death... . They are visible in the scene for a good few seconds before attention is drawn to them.
 * In Alfred Hitchcock's The Birds there's a scene where Tippi Hedren's character is sitting outside a school, and behind her we see one or two crows flying down to perch, and then a few more, and a few more, until one of them finally catches her eye and she turns to see hundreds of them perching on the playground climbing frame...
 * In the movie Don't Look Now, the main character is convinced that his daughter (who drowns in the opening) is alive and wandering around the town he is staying in. During the movie's events, background noise coming from nearby radios and televisions warn civilians about a serial killer terrorizing the town. When the man finally corners the apparition of his daughter,.
 * Ju-On, the Japanese horror film that spawned The Grudge, has a particularly unsettling scene in which the female lead is slowly exploring the haunted house. The camera turns with her to a foyer and stairs leading up. And if you aren't paying very careful attention, you probably won't notice anything unusual until the little boy's head peeking out from halfway up the stairs leans out of sight.
 * A classic scene from both the Japanese and American films is the lead in an elevator travelling up, with aforementioned little boy staring at her from the second floor. And the third floor. And the fourth floor. And the fifth floor...
 * Michael Myers just sort of appearing all over the place in Halloween.
 * A lot of the humor in Shaun of the Dead comes from background events to which the heroes are initially oblivious. The most startling example comes from the scenes where Shaun and Ed enter and exit The Winchester. When they enter, there is a couple making out by a phone booth. When Shaun and Ed leave, the couple is still there. Shaun and Ed make a note of this and go on their way, not noticing how one is being devoured.
 * Another oft-noted example contains an element of Ironic Echo - in two scenes, Shaun walks to his local supermarket, buys something, and walks back home. The first time, everything's normal. The second time, the street is trashed, and there's a lot of blood and dead bodies - some walking about - around the place. Shaun's equally oblivious both times.
 * In Friday the 13 th, one girl sees there's nothing there and says she must be going crazy, just as we see the shadow of an axe rising up behind her.
 * A double example in The Descent. Before the crash, you can see both the other car approaching and that their own car is drifting over the white line into the wrong lane.
 * In Spider-Man 3, the falls to earth while Peter and Mary Jane are macking on a giant web hammock.
 * The film Adaptation has a really heartbreaking one where the
 * A Fish Called Wanda has Otto spying in through the window on Archie and Wanda before entering the house. This doubles as a Funny Background Event.
 * In Darkness Falls, the evil Tooth Fairy (don't ask) pulls this trick when the good guys have made it to the top of the lighthouse. Everything seems okay to them, but after a moment we can see the monster out the window, drifting closer...
 * In the beginning of The League of Extraordinary Gentlemen, a man is pretending to be Allan Quatermain, while halfway through the conversation we can see Sean Connery, the real Quatermain, sitting in shadows just to his left. Eventually he turns around and tells the impostor to toddle off.


 * In The Dark Knight,  (or at least his hand) can be seen grabbing Maroni's passenger as Maroni gets in the car, before
 * In the Dario Argento film Deep Red, when the main characters enters the psychic's apartment after her murder, the murderer's face can briefly be seen in a mirror as he passes. He spends the rest of the movie trying to remember what he's seen, and doesn't put it together until the very end; nowadays, an alert viewer with a DVD and a pause button can figure it out immediately.
 * During the infamous rape scene in Irreversible, a figure in silhouette is seen entering the far end of the tunnel, watching the act in question for a few seconds, and walking away again. Hopefully it's to alert the police, but the movie's such a horrorshow it could just as easily be out of callous indifference.
 * Mr. Kreeg (Brian Cox) of Trick 'r Treat is one of the few horror movie characters to try to get out of his house when he knows that there's an intruder trying to kill him; in this case, Creepy Child Sam. Unfortunately for him, by the time he gets to the door, his hands are all cut up, and the door is covered in locks because he's a shut-in. So as he's trying to open all the latches with his cut-up hands while panicking... Sam comes crawling along the ceiling.
 * A subtle version can be seen in The Nightmare Before Christmas. While Oogie Boogie is taunting Sally and Santa Claus, if you look behind him, you can see Jack Skellington sneaking into the lair all spider-like.
 * In Oliver Stone's Alexander, Hephaistion's death scene: Alexander speaks with him, then goes to a window and makes a speech about his future conquests and their growing old together...meanwhile, in the background, very much out of focus, Hephaistion dies.
 * In the Stan Winston directed horror film Pumpkinhead there's a moment when a character walks across the room and we just see the titular monster walking past the window behind her.
 * Happens a lot in Coraline. Mr Bobinsky is often doing stuff in the background before the titular character notices him, as well as Wybie and the cat in the beginning. At one point, while Coraline's fighting yellow flowers, a bunch of bigger, blue flowers creep in from behind her. (It's very noticeable, though, because of the sounds and the very next scene is from the flowers' "point of view" crawling to her.)
 * The film The Strangers did this once. One of the killers just walked right into the house, a few feet behind the main character, with absolutely no fanfare. You might not actually notice him at first, and he leaves a shortly after entering. When you do notice him, it can be quite unsettling.
 * In Boiler Room, during the scene when Seth and Abby are talking in the car, you see the FBI agents pull up and start walking over (to arrest Seth) in the background quite a few minutes before it actually happens.
 * In the James Wan horror film Insidious Renai walks right by  on her way to the kitchen less than a minute before he actually appears.
 * In Back to The Future, in a scene where Doc and Marty are outside talking, a man on a bicycle passes by in the background. In the sequel, we learn that this is Doc from the future.
 * Probably a coincidence: the sequels weren't planned at the time of the first one and the movies aren't in a Stable Time Loop.
 * Or they could just be fanatics for detail and decided to Throw It In.
 * In a 'blink and you'll miss it' moment at the end of Thor, during the final fight between, the two are thrown from the sphere at the base of the Bifröst and one tumbles over the edge of the bridge. Look carefully and you'll see that, just beyond him, he's actually tumbling further and what's dangling over the edge is an illusion.
 * During the quidditch match in the first Harry Potter film, when Hermione looks at Snape and sees him muttering an incantation you can see Quirrell nearby doing the exact same thing.
 * In the 1973 film of Jesus Christ Superstar, during the song of Simon Zealotes, Roman soldiers can be seen gathering in larger numbers observing the commotion, and more meaningful, Judas is in the background visibly disturbed by the events, forcably walking off in the background during the next song, Poor Jerusuelum.

Literature

 * In The Dresden Files novel White Night, when Harry and Elaine are heading for Thomas' boat at the marina, there's mention of a boat with a particularly bad engine belching smoke. It gets passed off.
 * In the first book of Diane Duane's Young Wizards series, So You Want To Be a Wizard, has Nita waking up rather disappointed after she's taken the Wizard's Oath and nothing is different. Except a careful reader will notice that now 'Sun' is capitalized, even if not at the front of a sentence...
 * These show up occasionally in the Wheel of Time series. Sometimes a person (or persons) slipping into the scene is slipped into a paragraph. A paragraph or two later, someone notices that he (or they) are carrying knives. It's a gray man attack.
 * In Purple Hibiscus the main character's father is head of a newspaper that repeatedly refuses to censor its stories so the government looks better. It's very much out of focus until the main editor is

Live Action TV

 * In Ghostwatch, the evil poltergeist "Mr Pipes" can be seen several times at the back of a room, etc., meaning you could either jump or not notice it at all.
 * In the Community episode The Psychology of Letting Go, Abed has an ENTIRE SUBPLOT play out entirely in the background of other characters' stories - he meets and bonds with a pregnant girl, gets in a fight with her boyfriend, and delivers the baby. This is then lampshaded in a later Season 2 episode - when Shirley goes into labor, everyone is surprised to learn that Abed has experience with the situation.
 * The Buffy the Vampire Slayer Wham! Episode "The Body" is noted for its complete absence of any incidental music. This is used for great effect when Dawn goes into the morgue and a vampire silently rises in the background.
 * Also in "After Life", when Xander is on the phone to Willow and Anya after the, and just out of focus, we see.
 * Another example (Joss Whedon loves this trope) in "Conversations with Dead People" - Dawn is alone in the house, and strange things are happening. As she tries to figure out what's happening, the camera suddenly shifts angle, and we see in the background. Cue Scare Chord as she suddenly realizes what's behind her, and turns to see
 * On a subtler note,  can be seen in the background of a minor scene in the two episodes prior to his main appearance in the series, dancing in The Bronze the first time, and in class with our heroes the second.
 * In The Middleman there is a scene where the focus is on the Middleman speaking to his Mission Control, who is telling him that the Monster of the Week MUST be captured alive. In the background, the Middleman's sidekick is shown finding, fighting, and ultimately killing the fish. Really more of a Funny Background Event, but plot-relevant.
 * In ER, when Doctor Pratt was seeing off a patient up on the roof, there were two faint lights behind him. Then, when Pratt turned around, we see that the two lights collided. A commercial plane and a private jet had crashed.
 * In the Doctor Who episode Midnight, a videoscreen behind the Doctor briefly shows Rose mouthing his name. None of the characters notice. This is foreshadowing for the next episode.
 * Rose appearing unnoticed on video screens was one of the running themes for series 4 that replaced the Arc Words of the past three series, with her showing up at some point in nearly every issue.
 * Also in Doctor Who, The Waters of Mars: the first person to get infected by the Flood does so in the background of the shot with his back to us, with lots of jerking and writhing, so that we know something is wrong and are yelling for the character in the foreground to get out of there.
 * In Forest of the Dead, while the Doctor is talking to the Vashta Nerada, Other Dave says "We should go now, Doctor!" repeatedly. It turns out that he has been eaten, and the words are just his communication device ghosting.
 * In "The Time Of Angels", you can notice Amy occasionally slipping numbers into her dialog. It's so fast you'll have trouble noticing it, and you might not even pick up that she's counting down..
 * Spin-Off series Torchwood continues this - in the episode "Captain Jack Harkness", a "Vote Saxon" poster is seen on the dance hall door.
 * In Fringe every single episode has an observer in the background of an important scene.
 * In the Stargate SG-1 episode The Brocha Divide, you can see one of the Touched in the forest behind Daniel and Teal'c as they tend to the body of a woman. They actually attack a couple of minutes later.
 * Mad Men did this well with JFK's assassination as two men are in an office having a conversation with the TV on with very low volume. The report becomes a special report, but neither pay attention as they are busy in their conversation.
 * In the Firefly episode "Safe", while Simon and Kaylee are arguing in the general store, River can be observed in the background wandering away, setting up the rest of the episode.
 * In the episode "Objects in Space", while (almost) everyone's asleep, Serenity is boarded by a bounty hunter looking for River. The hunter's ship could actually be seen in the background in the previous episode, although its significance wasn't immediately apparent.
 * In the Season 2 premier of The West Wing, Josh is waiting for a plane when several Secret Service agents enter the frame around him, one-by-one. It takes a bit before the audience notices, but Josh doesn't until the President enters from offscreen.
 * In the mini-series Whitechapel the camera would often linger on a red-headed nurse who worked in the hospital that the investigators keep visiting. She ends up being.
 * The Lost episode The Other 48 Days opens with a beach scene. Several dots appear in the blue sky, which slowly get bigger and reveal themselves as the tail and other pieces of Oceanic Flight 815 hurtling towards the island.
 * In an early episode of True Blood, two characters are talking in the foreground. In the background, a hanging corpse is visible through a doorway for several minutes before the characters draw attention to it.
 * In the first episode of Kamen Rider Double, during Shotaro's phone conversation with Phillip, the Magma Dopant can be seen for a brief few seconds before Shotaro could bat an eye at it.
 * The Nanny did it once (combining with the humorous cousin): when Fran describes to Mr. Sheffield the reactions of children being disappointed by their parents, C.C. is on the patio acting out these symptoms on Niles. Then commented on by Fran "As seen in our audio-video theater production here."
 * In the How I Met Your Mother (Wham) episode "Bad News", numbers starting at 50 and counting down can be seen strewn about random locations throughout the entire episode. When the "countdown" finally hits zero,
 * In "Drumroll Please", behind Ted first seeing and falling in love with Victoria, you can see Marshall first tasting and falling in love with the best cake of his life; a comparison that comes up later in the episode.
 * In the final episode of the second season of The Sarah Connor Chronicles, during the confrontation between Weaver and the Connors in her office, one can see  out the window a few moments before it becomes very relevant.
 * In one episode of Boy Meets World, the characters are sitting around in the student center having a comedic conversation while Cory gets in a fight with his teacher in the patio outside. The event is brought to the foreground when Cory shoves the teacher through the doorway.
 * In Kaizoku Sentai Gokaiger episode 13, you can briefly see a man in a red shirt making the Monster of the Week obey a crosswalk sign. In the very next episode we learn that the man is Kyosuke Jinnai, former Carranger leader Red Racer and the focus of that particular episode.

New Media

 * Marble Hornets milks this for all it's worth. Many times in the videos Slender Man is visible in the background standing statue stiff and staring at the viewer. And except for Entry #7, no one ever notices him.
 * There is also Entry #12, where the cast seems to notice him but not his strange features.
 * Also, look very carefully at the window in Entry #19.
 * In the DVD Commentary, the creators joked that pretty much all of MH can be summed up as: "Agh! Look at the background!"
 * Slender Man's appearances anywhere.
 * There is a man hiding in the shadows during the video conversation in chapter 17 of Broken Saints..

Video Games

 * In BioShock (series), the first time you see a Little Sister Annex (the metal things built into the walls where Little Sisters come out of), there's one staring at you for a few moments. The object isn't a visual focal-point for the player, and quite a distance away from you when it happens, so many players miss it.
 * Psychonauts has these -
 * Multiple times throughout the scene where the Lungfish is attempting to fish for Lili and Raz.
 * Which doubles as a Funny Background Event, due to some of the things it uses to try and lure them in.
 * While ascending the insane asylum, it's easy not to notice the sobs or the flashes of a girl's image. (Unless you have subtitles on...)
 * Throughout the Meat Circus level, one might notice a strange blue apparition appearing randomly to scare the crap out of players.
 * Grand Theft Auto: San Andreas - During the Cutscene for the 'Wu Zi Mu' mission, a man in a black jacket and green jeans is sitting casually on a car in the background. That man is Claude, the player character of Grand Theft Auto III, who is Catalina's new boyfriend in the next mission and who gives CJ his car garage in San Fierro.
 * Most of the G-Man's appearances in Half Life. The first is even before all the trouble starts - you look through a window and see a scientist arguing with him.
 * Actually, you can see him even earlier, before you get off the tram.
 * The advisers can be seen in monitors throughout episode 1.
 * Well actually, the first one shows up on a monitor at the very end of Half-Life 2,
 * When Princess Peach's birthday cake is first seen in New Super Mario Bros. Wii, you may notice for a second that the 'decorations' are actually the hair/headgear of the Koopalings.
 * In Brutal Legend, upon arriving at the Kill Master's domain, there's a difficult to see event occurring just above the default camera position (and above the focal points of the scene):
 * In Call of Cthulhu (tabletop game): Dark Corners of the Earth there are several instances early in the game where you get visions of being watched. If you look in the right direction at the right moment, you may catch glimpses of your watchers on the rooftops, hinting at what's waiting for you later in the game. Also, if you look through certain windows in the starting area, you can see various disturbing sights, such as corpses being dragged away.
 * A number of suspense scenes from The Lost Crown have small yet creepy details in the background, like the face of an Ager brother looking on when.
 * A lot of plot points in Golden Sun games tend to be foreshadowed in NPC dialogue or thoughts, browsing through bookshelves in random houses, or the like.
 * In Rule of Rose, when Jennifer first goes up to the Old Mansion (first part of the intro), take a gander up at the roof region; most players miss it, but the airship's billowing form can be briefly (like 1 to 2 seconds) seen as a dark shadow overhead while a cloud passes in front.
 * Another scene that this happens is in the first half of the April chapter. You are given the task to find a beautiful butterfly in the background; after rescuing Brown, when you're doing 'Find' commands with him you will sometimes notice the little boy from the opening occasionally running by if you have Jennifer facing the camera. This sometimes serves as a reminder that the game's creepy as sin.
 * Several moments before the terrible Player Punch with  occurs, Wendy is visible in a window outside near the coffin (after the cut scene) if you rotate your camera around while walking in the orphanage.
 * During an early cutscene in the second No More Heroes game, a man falls from the sky and destroys a car across the street from where Travis and Sylvia are sitting, without even getting a notice or mention in their conversation. What at first seemed like a totally random incident turns out to be
 * In Kingdom Hearts II, Stitch can be seen crawling around the hidden laboratory a couple times before Goofy notices him on the ceiling.
 * Batman: Arkham City uses this five times in row during the opening. When the player first starts walking through into the city they can see Black Mask, one of the villians, getting forced into a corner by some guards. Shortly after while standing in line they see a prisoner that looks an awful lot like Deadshot standing in line and hear him say that Bruce Wayne is "on his list". Shortly after that as the player walks towards the gates they just barely see Azarel standing on the top of a nearby building. Soon after you get the batsuit you can ecounter a group of doctors, one of whom has been disfigured and is wearing bandages that make him look just like Hush. Finally during one of Joker's messages you can just barely hear someone that sounds oddly similar to the Joker coughing and whispering in the background.

Web Comics

 * This trope is the only reason this Order of the Stick page isn't filler. Elan tells Haley that he just found she was right about his father.
 * In this General Protection Fault comic, Fooker gets a call from his brother that turns out to be much more meaningful than he lets on.
 * In Drowtales, Shodun, a previously introduced character, appears briefly in the foreground of a scene, and then later shows up out of focus through several pages before coming into the foreground again, where she.

Web Original

 * In Final Fantasy III Trilogy, while the heroes are answering the bridge troll's questions, you can briefly see Kefka pull Celes offscreen and then replace her after taking her likeness.
 * In Red vs. Blue, in Season 2, Church and Tucker are having a conversation about something (this troper thinks it was about the "switch") and someone just runs by in Blue Base. In Season 3, it's revealed to be
 * Crosses over with a Funny Background Event in the first Tankmen cartoon. During one scene there's a gag in the background where we see a soldier get shot right after learning that he's about to have a son with his wife. It seems like just a minor one-off joke in the background. Over the course of the various Tankmen cartoons we learn who he was, how he joined the Tankmen, how he met Sgt. John Captain, his origins, some of his personality, and who killed him.

Western Animation

 * In the Futurama pilot, Nibbler's shadow can be seen for a split second after Fry falls into the cryogenic chamber. You'll have to be looking for it to notice. In another episode, Nibbler's eye can also be seen sticking out of a trashcan in a flashback. As with the shadow example, it's only there for a split second and you have to pay close attention to see it.
 * Used in X-Men: Evolution, not in terms of plot, but theme. After the kids are outed as mutants, there's an episode about whether mutants should be allowed to go to the same schools as 'normal' people. In the shot when they walk back into the school for the first time, there's a black kid in the background drinking from a water fountain; a clear nod to a rather less Fantastic Racism.
 * Sort of a "blink-and-you'll-miss-it" Easter Egg example appears in this promotional spot for Amphibia where Sasha interrupts the theme song to replace it with her own version. Pause at the 0:45 mark, and you can see Anne and Sprig fleeing from the giant chicken monster, a scene that is shown close-up at approximately the same time in the regular credits.

Real Life

 * Due to change blindness, you can miss this happening right in front of you, even if you are told it is happening, unless you are told exactly what you are looking for. Visit the University of Illinois Visual Cognition Lab and try the seven "Gradual changes to scenes" videos. You know in advance that something is being added or taken away from a scene you are watching, but many (most?) people will miss most of them.
 * There is also the Selective Attention Test video, in which two groups of people pass a basketball each back and forth, and half the audience is supposed to keep track of how many times one of the groups passed the ball. Most people fail to notice the guy in the gorilla suit walk in, thump his chest, and walk out partway through the video.
 * A similar test had students who volunteered for a survey who were met by a receptionist and given a form to fill out. This receptionist dropped a pen, bent down behind the counter to pick it up and a completely different person stood up and continued the conversation. A large number of the participants didn't notice.
 * This trope was how a purse snatcher got nabbed.
 * A Tampa reporter was filing a report about high gas prices when two cars had a serious collision in the intersection right behind her. The anchorwoman deadpanned: "They must have been shocked by the gas prices."