It's Probably Nothing

... except it is something!

One of the heroes receives a broad hint that something unpleasant might happen—any kind of bad thing, from the plans of a Mole to a debilitating disease. It could come in the form of a prophecy, an important clue picked up off a defeated enemy, an inconclusive medical test... the form varies depending on the context.

In a classic example of Genre Blindness, the hero carefully evaluates the hint and concludes almost immediately that it is most likely meaningless, regardless of the reliability of its source. And he will keep doing that even though additional, corroborating hints start showing up, until it is almost too late.

Because if he didn't, he'd solve the mystery, foil the criminal, or seek out proper treatment in the first act of the show, and then where would we be for the next forty-five minutes?

Which is why, on the rare circumstance that the hero does go after it—it proves to be a Red Herring.

Many security guards (especially in video games, for gameplay reasons) are prone to this as well. Hearing a noise or seeing something out of the corner of their eye, they'll investigate for a moment, or their "more experienced" partner will tell them it's just a rat, or a stray dog, or something else innocuous, and say something along the lines of "It's probably nothing". At which point they get knocked out/captured/killed/eaten. (See The Guards Must Be Crazy.)

This is an instance of someone holding the Idiot Ball, provided the event is out of the ordinary in some way. Expect The Great Detective to berate the fool for his casual dismissal of the occurrence, probably during The Reveal.

Possibly the opposite of a Cat Scare. Not to be confused with Within Parameters, which is related. Also related to Convenient Decoy Cat.

A case of some Truth in Television as each area has a large assortment of ambient sounds that individuals become familiar with and often ignore possibly at their detriment.

Anime & Manga
"Genma: What's that? Soun: The wind, probably."
 * The Yu-Gi-Oh the Abridged Series example, as well as the original; Tristan somehow manages to sneak up on a guard while wearing a full suit of plate armor for no well-defined reason.
 * In the Abridged Series, it's because of the Rule of Funny.
 * Played with in the Sonic the Hedgehog movie. Sonic is relaxing on the beach and Tails goes out to the ocean to try his new machine, it goes out of control and he begins screaming for Sonic to help him. Sonic, who just wants to relax, dismisses it as "probably nothing". Tails continues screaming for Sonic, and he finally yells at him to shut up.
 * Played straight in Fullmetal Alchemist when anytime the plot calls on Alphonse to rescue Ed, you are almost guaranteed a scene with a giant suit of armor sneaking around.
 * Let's not forget when Edward asked, he and his brother busted out laughing at how ridiculous that sounded.
 * In the Yotsuba Arc of Death Note,
 * Ranma 1/2:

Fan Works

 * In a chapter of Pokémists: Pocket Alchemists, a Fullmetal Alchemist fanfic, the four main characters stumble into an enemy meeting by breaking through the wall, and the bad guys in the meeting assume it was the rain. They keep assuming it is the rain even when the good guys talk at normal volume and even yell "You people are...IDIOTS!" The bad guys finally notice the good guys because one of them SNEEZES.
 * In the Firefly / Doctor Who crossover fanfic The Man with No Name, while some of the Serenity crew is hunting Reavers in some woods, they all suddenly stop, thinking they heard something. The Doctor opts to barrel through anyway. Guess what he walks right into?
 * In the Yu-Gi-Oh! fanfic Decks Fall Everyone Dies, Joey ignores the fact that he is coughing up blood while thinking this.

Films -- Live Action

 * Used at least twice in Star Wars. In A New Hope, Obi-Wan uses it against two stormtroopers on the Death Star to cover his escape. In Revenge of the Sith, two Super Battle Droids are investigating the crashed Jedi starfighters in the hangar bay. When one hears Artoo lurking in a corner, the other stops him, saying it's nothing.
 * Of course, if the Stormtroopers had actually checked out the sound, it would have been even more useful for Kenobi. As it was, they didn't notice him moving even though he had only gone about three inches by the time they turned back to their original positions.
 * Wasn't that because he was using the Force?
 * They probably can't see a thing in those helmets.
 * After the characters watch Star Wars 4-6 in Spaced, Tim declares that entire plot wouldn't have happened if the Imperial gunner in A New Hope hadn't dismissed the escape pod carrying R2D2 and C3PO down to Tatooine as nothing to worry about.
 * Humourously referenced in Family Guy: Blue Harvest. "Wait, hold your fire, there are no life forms aboard that vessel", "Wait, hold your fire? What, are we paying by the laser now?" "Hey Terry, you don't do the budget but I DO."
 * Spider-Man 3, when Marko's presence in the test chamber is immediately dismissed as just a bird.
 * Played with in Pan's Labyrinth. Early in the movie, Ofelia hears some creepy noises coming from the walls of the house at night, and her mother explains it as the sounds of the house settling. Later,
 * Played with? More like Fridge Horror.
 * In Duck Soup, spy Harpo thinks he's opening a wall safe, instead turning on a radio that plays loud brass band music. Groucho's explanation for the sudden noise: "Sounds to me like mice!"

Literature

 * James Ellroy typically does quite a convincing job of this, as we really can't blame the cops a lot of times for ignoring details that genuinely seem inconsequential. It's their bad luck that they're being written by a guy who loves coming up with insanely complicated stories where every little detail matters.
 * In the Grimm's Fairly Tales version of Hansel and Gretel, the title siblings hear a voice from within the house, but remark "Never mind, it is the wind."
 * In the Solomon Kane story Footfalls Within, by Robert E. Howard, the titular footfalls are blithely dismissed as "nothing" by a bunch of slavers, with foreseeable consequences.
 * This is actually quite reasonable of them, mind you - not only do the alleged footfalls come from within a massive stone structure evidently sealed shut for hundreds or thousands of years, they have no sane reason to trust the man who tells them, nobody but him can hear the sound (they do try), and indeed there is no sane way for it to be heard through the solid stone walls. Karmic Death? Oh yeah. Genre Blindness? Well, sure. Idiot Ball? Not at all.
 * In Remnants, the programmer of a computer-based perimeter security system puts in a backdoor—the program assumes that any intruder emitting a certain high-pitched tone is a wild pig. This is very useful when he needs to
 * A Series of Unfortunate Events: "If there's nothing out there, then what was that noise?"
 * Here's a fun Drinking Game: Take a sip every time someone in The Mysteries of Udolpho (1794) says, "It's only the wind" or something like.
 * In the Warrior Cats novel The Forgotten Warrior, Tigerheart warns Dovewing that Dawnpelt, but she brushes it off as nothing several times. Near the climax of the book,

Live Action TV
"Natalie: What was that noise? Yuri: It was probably just a car on the highway. Crow T. Robot: Yes, a car that sounds just like a wolf."
 * Mystery Science Theater 3000, episode 904 "Werewolf":

"Steve: It's probably just the wind. Stephanie: Just the wind? Just the wind?! It's never JUST THE WIND!"
 * Full House:

""That ain't the wind. As much as we'd like it to be... it ain't.""
 * In the Buffy episode "Doomed", Giles dismisses an earthquake as "shifting landmasses". On the one hand, he is in Southern California. On the other hand, as Buffy points out, the last time they had a decent earthquake in Sunnydale, she died. Buffy is proven right, as it turns out to be a portent of the apocalypse.
 * The Twilight Zone, "The Purple Testament", three wounded soldiers conclude that the "explosion" sound must just be thunder.
 * In the mini-series Shackleton, after the Endurance is trapped in the Antarctic ice, the crew hears an ominous grinding sound and feels the ship move. Shackleton (Kenneth Branagh) insists that it's the result of a whale mistaking the ship for a hole in the ice. It isn't.
 * Power Rangers Dino Thunder: In the first episode, the three soon-to-be-Rangers hear the Mooks of the year coming for them. Kira suggests (without much hope) that it's the wind, and Ethan proves his Genre Savvy by disagreeing.

Poetry
"While I nodded, nearly napping, suddenly there came a tapping, As of some one gently rapping, rapping at my chamber door. "'Tis some visiter," I muttered, "tapping at my chamber door— Only this, and nothing more.""
 * The Raven by Edgar Allan Poe:

Tabletop Games
""More of that strange oil...It's probably nothing.""
 * Magic: The Gathering:
 * In Scars of Mirrodin, we get Steady Progress' flavor text, invoking the trope by name in reference to Phyrexian oil, which is slowly spreading The Corruption throughout Mirrodin:


 * In Innistrad, plane filled with horror tropes, we get Bump in the Night and Feeling of Dread.

Theater
"All: (much alarmed) Goodness me! Why, what was that? Dick: Silent be, it was the cat! All: (reassured) It was--it was the cat! Captain: (producing cat o' nine tails) They're right, it was the cat!"
 * Gilbert and Sullivan inflicted this on the entire crew of HMS Pinafore as they try to sneak the eloping lovers off the ship:


 * The Pirates of Penzance, by the same team, has the song "With Catlike Tread". The titular pirates, while sneaking into Major-General Stanley's estate, sing at the top of their lungs about how they're being silent. The very next song starts with the Major-General mentioning that he "thought I heard a noise", and concluding that "it must have been the sighing of the breeze." (Pirates was, at the time of its release, criticized for having the same plot as Pinafore.)
 * Better yet, the Pirates and Policemen are making loud comments in the background "He though he heard a noise. HA HA!" and then join in his song "Sighing Softly To The River" without him catching on right up until the finale kicks in.
 * A famous operatic example is the scene in Hansel and Gretel where the children are busily taking pieces off the Gingerbread House and eating them. Twice, a voice from inside demands to know who's been nibbling at her house, the children think for a moment, and they declare it was the wind, the heavenly child.

Video Games
"Uh... it's probably not a problem... probably... but I'm showing a small discrepancy in the-- well, no, it's well within acceptable bounds again. Sustaining sequence."
 * The staple of the Stealth Based Game, or rather, any game with a stealth element.
 * Half-Life is probably the trope namer for this one.

"Dome: Yeah right, when was the last time the wind said hostiles!, to you?"
 * In the game Tenchu, fighting a guard automatically raises the alarm. Guards who were, just a moment ago, attacked with katanas will dismiss the incident as being caused by a dog!
 * This is one of the more common and ridiculous occurrences in the Tenchu series. In Wrath of Heaven you can drop down on one guards head, snap his neck with a sickening sound in front of another guard, then as the guard pursues, jump up on a roof and hide, only to hear the guard pause and say "Ah forget it."
 * The guards in Thief do this a lot. Torch that's been clearly doused with a water arrow, presumably leaving puddles of water all over the place? "Must've been the wind." Large metal object falling down, making a stupid amount of noise? "Hmm... must be my imagination." Et cetera.
 * The AI in Oblivion does this to the point that it is just sad (e.g., dismising an arrow in their back as the wind) especially when the AI was something that was hyped up to no end before the game was released.
 * Even worse, they won't even react if their buddy's corpse is lying next to them. But move a little too close to them and they start charging at you.
 * In all fairness to the AI, a guardsman or legionary who happens upon a stealthily murdered corpse will examine the body and comment on the likelihood of the killer being in the vicinity... before continuing with their regularly scripted lives.
 * Then again, I once witnessed a bug where some guards suddenly fought each other. One of them died, and the other immediately bent down and examined who he'd just killed, saying "The body is still warm, the killer must be nearby." No Shit!
 * Likewise, in Beyond Good and Evil you can hit a guard in his air tank—and the other guards will just fix the tank and declare "false alarm".
 * Averted in Robin Hood: The Legend of Sherwood. Guards always check every noise, explore every inch of the room, will free anyone who was tied up, and will report corpses that they haven't already seen to their captain.
 * Averted in Metal Gear Solid, where guards would always check to make sure it's actually "nothing". The ones in Metal Gear Solid 2 would actually search every nook and cranny of the room you were seen disappearing into, and even if they don't find you, extra guards would be sent to patrol that sector.
 * Then again, after the guards investigate something, they'll eventually decide It's Probably Nothing and wander off... even if "nothing" was being shot. Guards will always say It's Probably Nothing when they wake up from being knocked out, even if they were knocked out by being shot in the face with a tranquilizer dart while radioing for help. Sometimes a guard will decide It's Probably Nothing when he finds another guard dead in a puddle of blood, since there's nobody around to have killed him. He'll radio for help, they'll do a half-hearted sweep, and leave.
 * Crazy as it sounds, this is actually a rather smart thing to do (short of dismissing getting shot, that's just weapons-grade retarded). A guard is knocked unconscious by an intruder. The guard is then found and revived, causing the other guards to call for back up. But, the guards have no clue if the intruder is still in the area. After the sweep with the extra guards turns up nothing, they're told to keep alert, but go back to their normal patrols, under the assumption that the intruder is no longer in the area. It may be the wrong assumption, but there's no faulting the logic.
 * The guards in Metal Gear Solid 3: Snake Eater play this straight sometimes. If they get a glimpse of you from a distance, they'll pull out a pair of binoculars to get a closer look. If you hide yourself quickly enough, they'll think it was "just their imagination".
 * Splinter Cell has guards as thorough as (if not more so than) the ones in Metal Gear Solid. Worse, they have far too many ways to remove the shadows you rely on. The guards early in the game have flashlights and flares. The Chinese soldiers have headband-mounted lights. Not to be outdone, the Georgian Special Forces have night-vision goggles. By the third game, enemies with thermal-vision start showing up, complete with x-ray vision.
 * Of course there are still mooks who have no special way of seeing in the dark, and they fit the trope perfectly. There is a co-op level in Chaos Theory where you can enter a room with two guards watching a sports game on TV. Shooting out the TV then quickly leaving the room results in them waldering around for a bit, then going back to the couch with a 'probably the wind' comment and watching their shot out TV. Good job guards.
 * This is actually Lampshaded by the enemies: if the player makes a loud enough noise without being seen, there's a randomly-occuring exchange where one guard says "It's probably--" but is then abruptly cut off by his partner, who tells him that it's never "just nothing".
 * In the first Predator stage of the original Alien vs. Predator PC game, after gibbing a guard in the opening cutscene, you can hear the base's Mission Control: "Unit Two, report in... Report in, Unit Two... Unit Two, do you copy?! Damn, his comm must be down." You're doing these idiots a favor when you kill them.
 * Deus Ex averts this slightly. Guards will first investigate, then wonder where you are, before deciding you aren't around—but it takes all of ten seconds. Often they can be heard to utter "He's miles away by now" when J.C. hides behind a box in a dead end.
 * If you shoot a guard in the face with a tranquilizer dart and hide, he'll run around for a moment, then (because the drug in one dart isn't enough to knock them out) return to his patrol with the arrow sticking out of his face.
 * In a Shout-Out to this trope, the very nastiest event in Europa Universalis 2 ("The White Lotus Rebellion") has two options, one of which "It's likely just harmless talk." (Cue 30% revolt-risk.) The OTHER option gives you half that revolt-risk, but costs you an arm and a leg.
 * Averted in Death to Spies. If any enemy even spots a body, sees the player for too long, hears any noise (except the silenced pistol), or if the player has any visible Soviet gear on at all—even after changing uniform --, has a weapon out (unless dressed as a patrolman, and then only a weapon that the others have, usually an MP-40), is doing something that doesn't match the disguise's purpose or rank (stealing a truck without being in an officer or driver's uniform) or is a patrolman/officer who can recognize if you are not one of them, they will almost immediately upon entering their "sight confirmation" begin to fire, alerting any other nearby guards, and giving chase, usually for half of the map. In many cases, they will run to hit the alarm, which will effectively end the mission because every guard in the area will be alerted to you (often well over 20-30 people), and quickly open fire if they spot you as well as give chase, often killing you very quickly if there are any sharpshooters in the area, even faster if you are headshot. Oh, and don't try hiding: they'll stay on full alert, just waiting for the chance to find you.
 * Notably averted by the 2009 Ghostbusters game. Even when the PKE meter shows nothing, the Ghostbusters never assume that It's Probably Nothing. They always investigate. Of course, blowing up  early in the game probably has them on their toes for the rest.
 * Lampshaded and subverted in Gears of War, where Dom does not brush off the strange sound so easily. He's right.

""Must have been ze vind.""
 * Usually averted in Fallout 3. If hostile guards hear you, they investigate, and raise the alarm if they see you. If you're well hidden, though, the other guards will berate the first for crying wolf.
 * With high enough sneak and a stealth boy or Chinese Stealth armor, guards will react in this fashion even after being stabbed. Repeatedly.
 * The Phantoms in The Legend of Zelda: Phantom Hourglass: Once Link enters a safe-zone, he becomes invisible to them. No matter how clearly in their sight he was before that and how long they've been chasing him before he escaped, afterwards, after looking around for barely two seconds in a "Where'd he go?" fashion, they apparently dismiss it as "It was probably nothing" and turn around to start patrolling their regular route again, without even considering to keep an eye on the spot where he disappeared.
 * Justified in that they're magical constructs with probably rather limited intelligence. Similar to babies the Phantoms likely lack object permanence, so once Link is invisible they cease to recognise his existence.
 * The military in Prototype. There's a shape-shifter on the loose with extraordinary powers. Your commanding officer just ran straight up a building, and then started gliding through the air. If your response is "He may be around here", congratulations, you're apparently qualified for the military.
 * Oh, but it's far worse than that. Entering said building, said officer develops a nasty habit of sneaking up on people, following them behind boxes (out from behind which only one person leaves, and it's not an officer) and moving said boxes and cars. Probably for privacy. Not only that, but after said officer enters the building, you can guarantee that shape-shifter is inside as well. After all, surely a "legit" soldier pointing his finger at a not-so-legit soldier and claiming that This is the creep! cannot be wrong...
 * By this point the entire building is almost empty. Oddly enough, this one guy keeps walking around and sneaking up behind people, kinda like that officer... Nah, it's just my imaginati-CRUNCH. Nom-nom-nom.
 * Letting him sneak around is probably more cost effective. Just let him take what he wants or he'll kill everyone and then take it.
 * The Great Escape plays this to the point of ridiculousness. Having charged through a door and straight into the arms of a patroling German soldier, you dash straight into another room leaving the poor sod gawping after you. His words?

"Guard (seeing Ezio hanging on a wall): What is he doing? Bah! I can't be bothered with this now! Seconds later, after the patrol passes, the nearby target gets two hidden blades in the chest"
 * Touhou Project character Koishi Komeji, as a satori with psychic powers to read the conscious mind of others that she disabled by giving herself a Poke in the Third Eye found out she suddenly gained powers over the subconscoius mind that effectively made her impossible to recognize or notice. While not exactly an Invisibility Cloak, she could be standing in broad daylight, rummaging through people's pockets, and nobody would notice she was there. She used this power to live as a functional hobo and a thief, stealing food and trespassing to sleep in people's homes.
 * This power is also used in a strange way by the oni Suika, whose ability of "gathering" lets her divide herself into mini-Suikas so small they are a functional mist, and give suggestions to others as subtle mind control to form gatherings (as well as send out mini-Suikas that steal food and alcohol for her gatherings). Almost nobody could figure out why they kept meeting, and dismissed the idea as simple whims of many people to do the same thing at once, although a few had the ability to recognize the mist for what sort of thing it was, if not the perpetrator or her motives.
 * Subverted in Fire Emblem Radiant Dawn when the hero is hiding with her pet bird in a hole. The bird chirps and the guard notice. She lets the bird go as they are about to investigate and it flies out of the hole. The guards shrug, saying it was just a bird and our hero sighs a sigh of relief. Then the guards capture her and go "you didn't think we'd really fall for that, did you?" Of course, another hero shows up to save our first hero.
 * Taken to the point of utter farce in Tales of Symphonia.
 * Repeated quite ridiculously in a later game of the series, Tales of the Abyss. Jade(by far the worst offender), Tear, Guy, Ion and even Luke himself all gasp or draw attention to themselves only to say "No, it's nothing." It's *always* something. Always.
 * Subverted in Assassin's Creed Brotherhood. Ezio had been told earlier that the men of Monteriggioni would be practising with the cannons at dawn, so his first thought when he hears cannon fire is that it is a training exercise. Then a cannonball goes through his room.
 * A version of this can also be seen throughout the game with the guards as long as you're not in a restricted area or actually on the roof/in sight of a roof guard.


 * In World of Warcraft, when your character is bitten by a Worgen, you dismiss it as just a scratch and nothing to be worried about. The end result of this is being taken by the transformation during a last stand, killing the allies unfortunate enough to not also be infected, and causing your final defenses to fall.
 * Five Nights at Freddy's: Security Breach; in one part of the game, if Gregory approaches Roxy's room, the player will hear her sobbing over her inability to catch him, trying to convince herself she is "not a loser!" Naturally, if Gregory moves too close to her, she will notice him and attack, but if he gets slightly less close with the flashlight on, she instead says, "Who's there?" and then, "It's nothing, don't get distracted!" and then leaves out the other door, leaving Gregory to search her room at his leisure.

Web Comics
"Legs: Tac isn't very useful without more data. (more than 100 pages later) Ebbirnoth: Metallic chitin and reflective wings... the scanner filed them as "chaff" and ignored them."
 * Schlock Mercenary has a few.
 * Right before Brad's freight shuttle exploded (they did this on purpose).
 * Toughs learned why recognition in an unknown environment must not be left to computers that aren't true AI. Schlock noticed an incoming swarm of bugs. First seen shredding a huge flying critter like it caught a burst from autocannon. Why the team learns about this from visual observation? Well...

"Anxiety Attack Pro-Tip: telling yourself "oh, it's probably just..." yields a terrifying list of things that are worse."
 * Later, from Howard Tayler's twitter:

Web Originals
"67. No matter how many shorts we have in the system, my guards will be instructed to treat every surveillance camera malfunction as a full-scale emergency."
 * Addressed in the Evil Overlord List:

"39. If I'm sitting in my camp, hear a twig snap, start to investigate, then encounter a small woodland creature, I will send out some scouts anyway just to be on the safe side. (If they disappear into the foliage, I will not send out another patrol; I will break out the napalm.)"
 * Evil Overlord List Cellblock A:

""What was that? ...Probably just the wind. Stupid wind: breaking a twig, creeping up behind me, breathing real heavy-like...""
 * Agent Wyoming's introduction in Red vs. Blue is full of this trope

Western Animation
"Stan: What was that? Francine: Probably just a loud noise."
 * Inverted in Code Lyoko, when Jérémie gets an anomalous alert on the computer and instantly thinks, "It's probably bad news."
 * Family Guy: In one gag, Lois and Peter mention in passing the giant squid in the kitchen which they absolutely must ignore. It promptly swats all the dishware off the table, prompting them to quickly remark "earthquake!" and "uhh, truck passing by".
 * Used, bizarrely, between two SWATbots—who you would think would have no business having separate thoughts—in an episode of the Sonic the Hedgehog cartoon.
 * Minimum AI necessary for guard units likely to encounter crafty intruders + Possibility of differing age/experience/previous assignments = Difference in thought/processing patterns.
 * Star Wars: Clone Wars plays this one for laughs, with Palpatine dismissing Grievous' clanking footsteps drawing nearer and then suddenly stopping, to the dismay of his Jedi protectors. Of course, the droid general's head appears in the window behind him even as he's delivering the line, hanging upside down on the outside of the building. One gets the impression that the scheming dark lord, who actually wants to be captured, plays the classic part with some glee.
 * Then again, the Ham is Large with this one.
 * Used for a plot point in Ben10's "Perfect Day": Max says this about the the Omnitrix acting up, but let's just say that he's not as he seems.
 * American Dad: When Haley tries to sneak in past curfew in "Bush Comes to Dinner":


 * Zigzagged in one episode of the second six part G.I. Joe mini-series. When Stormshadow approaches the Joes' HQ to steal part of the Weather Dominator, one of the Joes on guard duty asks another if he hears anything; the guy responds, "No, that's what bothers me." Stormshadow manages to get past them, to the vault, using knockout gas to disable the guards there. Then the guard outside who spoke before seems to notice, tells the others he's "not hearing it again" and they go investigate. Unfortunately, by then Stormshadow has stolen it and gotten away.

Real Life

 * Truth in Television—because, let's face it, when you hear a crack of a stick in the woods, the first thought that goes through your head is: "What's that?" and then when you look around and don't see a monstrous man-eating lady-killing psychotic freak of the beyond, you really don't try to linger on what kind of unspeakable horrors might be sneaking up on you right no... eh... AAAAAAAAAAAAAAAAAAAAAAAAAAAAAARRRRRRCH!
 * The sounds made in your house at night comes from the fact that the house is actually shrinking a little bit due to how it's colder at night than at day—like how the best way to open a resilient jar is to run the lid under some hot water, causing it to expand and be easier to open.
 * Also some spooky sounds from the kitchen or street in the middle of the night—it's very probably only a falling towel or a bird respectively; but in a horror movie you'd think "Why the hell doesn't he get the hell out of there!!??"
 * That creepy tapping sound you hear at night is almost certainly a particular type of harmless beetle with the oh-so-reassuring name of the Deathwatch Beetle.
 * It Gets Worse when you are on a ship, which is basically a very large building made primarily from metal, which expands and contracts much more than does the wood that houses are typically made from. As you try to go to sleep at night, the entire ship is groaning and creaking and making weird sounds as the many metal parts contract and pull against each other. Sleep well.
 * Not to mention just sounds in a place you are unfamiliar with. To someone who hasn't gotten entirely bored with the novelty of air travel, a jet liner is incredibly noisy, what with the hums and the whines and the buzzes and the clanks and thumps and beeping sounds on the intercom. The sound of flaps lowering before landing can be particularly unsettling, combined with the plane banking and turning as it lines up its approach with a narrow concrete strip at several hundred knots. Not to mention the very unsettling sound you hear when the plane gets close enough to the ground for you to hear the sound of the engines echoing off the surface.
 * It would actually be more worrisome if, when trying to sleep on a plane, there was suddenly no sound at all.
 * Anyone who has spent any time working, rather than travelling as a passenger, on a ship will attest to the fact that sudden silence will snap you wide awake in a second, as it indicates that the ship has suffered, at best, an electrical failure, and the possibilities get worse from there.
 * Averted by real life security personnel, who ideally will treat all alarms as real. Having a large number of false alarms can cause major problems.
 * Radar spotted the Japanese planes heading in to attack Pearl Harbor, but it was a new technology and the radar station was still in training mode and wasn't fully operational yet. The person the radar operators tried to warn decided what was actually a huge armada of incoming planes must be a handful of American B-17s scheduled to arrive that day, and the radar operators themselves didn't know enough about their own equipment to be able to say "Sir, that's ridiculous!"
 * Michael Shermer discusses in his 2010 TED lecture why humans are prone to suspecting any odd event as extraordinary, dangerous and intentional, hence dismissal of them as mundane is the exception, due to deconditioning. He also explains why Skepticism Failure is often the norm in reality, not the exception.
 * Any pet owner could easily blame a noise on the cat/dog knocking something over. Even the rustling of a gerbil could be taken for granted.
 * There are many people who invoke this by leaving their TVs or music sets on in the background, even when they go to sleep, so that they can be reassured of the movements and sounds instead of freaking out and jumping at shadows.
 * Played thankfully straight several times by both Soviet and Western radar operators during the Cold War. Several times the computers malfunctioned and detected massive nuclear attacks from the enemy. Every time the operators (correctly) dismissed this as a bug.