Astonishingly Appropriate Interruption

A humorous device used when a character is talking to another, but suddenly sees something which causes him or her to have a sudden and loud change of subject. However, astonishingly, what the distracted character actually shouts could well be what they had been about to say, due to double meanings of words or just plain old coincidence.

A variant of this is when the conversation after the change of subject is not what the speaker had been about to say, or the interrupter is another person, but the two parts still make perfect sense as a sentence when pieced together.

See also Last-Second Word Swap, where this is (usually) deliberately invoked by the speaker to avoid saying something for whatever reason.

Advertising

 * A commercial in New Zealand some years back featured someone constantly switching TV channels, and all of the dialogue we actually hear on each channel logically joined up with the dialogue in the next. For instance, on one channel we hear "an old hag!" (it was a soap opera or sitcom), the channel changes, and the very next thing we hear is "with six legs and a thorax" (a nature documentary on insects). It just continued like this.
 * A visual and unintentional example due to unfortunate sign placement, where an anti-smoking ad on a bus inadvertently encourages children to quit school.

Comics
"Superhero: I will save them! With my nerves of steel, muscles of iron- Chef: -and a knob of butter- Policeman: -it looks like we got here just in time for a- Superhero: -Jimmy down the liftshaft?"
 * Due to the panel layout in comic books, the variant is very easy to pull off. For example, a British comic had each panel a different channel, as per the Advertising example above, leading to exchanges such as:

"Treat your cat to... Miller Lite... Chlorox bleach... gets dentures bright... Turtle Wax... stops jock itch fast... Tootsie Rolls... are built to last... Cutty Sark... protects your car... Levis... give you lower tar... Banish grey with... roll on Ban... Keds... now in a six ounce can... Chevy's got... a lighter smoke... Cleaner people bathe with... Coke... Schlitz... for those who watch their weight... And Ex-Lax... makes the going great"
 * Mad Magazine did an 'ultimate rhyming advertisement' by overlapping real advertising slogans:


 * Advertisement placement can sometimes do this as well. A memorable one is in Peter David's Captain Marvel run, when Entropy first appears. He appears off-panel, speaking to Captain Marvel, when the reader turns the page, it's a full page advertisement for Stuart Little.

Fan Fiction

 * This sketch-like Sailor Moon fic, in which the setting is the time guardian Sailor Pluto deciding to take peeks at her friends' lives on Earth in a TV channel-surfing style.

Film -- Animated
"Naveen: My family cut me off for being a (sees leech attached to his elbow) LEECH!"
 * In The Princess and the Frog, Naveen has just landed in a swamp, and he is explaining to Tiana about why he is penniless although a prince.

"Jenna: Each one of our children have their own lives to live. It's our job to love them, and then... Boris (being chewed on by the puppies): LET GO!!!"
 * Shaun of the Dead has an example similar to the Mad Magazine entry above, as well as Ed interrupting a quasi-lover's quarrel with appropriate annoyed grunts.
 * The Simpsons Movie: "What kind of father wouldn't care about... A PIG WEARING A HAT!"
 * Monsters, Inc..: Mike is wooing Celia over dinner, telling her: "Just the other day, someone asked me who is the most beautiful girl in all of Monstropolis, and I said...(Mike notices Sullivan peeking through the window) Sully?" Celia is understandably not too pleased.
 * The Iron Giant: Hogarth's prayer includes several examples of this, but he keeps finding ways to fit his sudden shouts into his prayer.
 * Sitting at the dinner table, he looks over his mom's shoulder and sees the giant's hand in the kitchen. "Oh my God! Uh- Oh, my God, we thank you for this food. And- STOP! ...the devil... from doing bad things?" Then Hogarth sees the giant's arm crawling through the kitchen over his mom's shoulder and he yells, "GET OUT OF HERE- ... Satan..."
 * In Balto: Wolf Quest, Balto is reluctant to give his and Jenna's puppies up for adoption. He discusses his feelings with her while said puppies and Boris the snow goose are playing in the background.

"Fiona: When one lives alone, one has to know these things in case there's... there's an arrow in your butt! Shrek: What? (looks to see that indeed, there is an arrow sticking out of his backside) Oh, will you look at that."
 * From Shrek:

"Skinner: You know what I think, Linguini? I think you are a sneaking, overreaching, little...(gasps as he spots Rémy) RAT!!!"
 * Ratatouille:

"Al Gore: Here's to four years of clean air, clean government, and amazing new technologies such as-- (Bender appears) Robot!"
 * In the first Futurama movie:

Film -- Live Action
""We will now read from the Gospels of Matthew, Mark, Luke and... Duck!""
 * Blazing Saddles: The preacher is commencing his sermon when a bundle of dynamite is thrown through the window:

"Lord Dargis: (I am taken) myself by you. Oh, don't mind me. I'm just an incorrigible old... (sees Garfield) cat?"
 * Garfield 2. Lord Dargis has got rid of Prince (the cat), when Garfield, who looks exactly like Prince, settled in castle. This moment is priceless. Lord Dargis walks with his investor (charming young woman).

"Kermit: Um... motorcycle cop. Piggy: "Motorcycle cop" is a sweet nothing? Kermit: A motorcycle cop is chasing us!"
 * In The Muppet Movie, Piggy asks Kermit to whisper sweet nothings in her ear:

"Costas: You afraid that I will make fuck to you. But I only ask you to come on boat. Different thing. Boat is boat. Fuck is... (Sees Shirley) ...Fuck."
 * Scott Pilgrim vs. the World: "I don't think that anything will get in the way of how I- Shit!"
 * Shaun of the Dead has another TV-channel version. While Shaun is channel-surfing, the news reports on the zombies combine with various others to describe zombie attacks: "BODIES ON THE STREETS" *click* "with increasing reports of" *click* "people who are literally being" *click* "eaten alive." etc
 * In Shirley Valentine, Shirley walks on tavern owner Costas trying to seduce a tourist with the same lines he used on Shirley earlier.

"Minister: "Dearly beloved, we are gathered here today to witness Princess Vespa, daughter of King Roland...going right past the altar, heading down the ramp and out the door!" Minister: "We are here to join these two together in holy--MOLY!!""
 * Spaceballs: The Minister is interrupted during the wedding...twice:

"Jenny: And the first thing we're gonna do today is... Buffy! Xander: Did I fall asleep already?"
 * In Buffy:

Literature

 * Anne of Green Gables uses the "not what they had been about to say" version when Matthew first drives Anne to Green Gables. She is pretty much talking non-stop, and gets to: "...and Mrs. Spencer says...(sees an incredibly beautiful spread of apple trees in bloom) Oh, Mr. Cuthbert! Oh, Mr. Cuthbert! Oh, Mr. Cuthbert!" The narrator even lampshades the trope by pointing out: "This is not what Mrs. Spencer had said."
 * Dave Barry had an article that consisted of nothing but this. It's written in first person as Dave is scanning the radio looking for a good song, and as the stations switch between Insane Proprietor ads, strange Bible readings, and even stranger political ads, the transitions are almost seamless.

Live Action TV
"Natalie Teeger: Maybe the Captain saw something... [Randy turns around, revealing that he has grown a mustache] ...unusual. What is that? Lt. Randall Disher: What? Natalie Teeger: On your face! On your lip! Adrian Monk: It looks a little bit like a mustache. Lt. Randall Disher: Well, I'm in charge. It comes with the job. [Monk and Natalie continue to stare at him, dumbstruck] Okay, you're making me a little uncomfortable. Natalie Teeger: You're making me a little uncomfortable!"
 * Venezuelan Sketch Show Cheverisimo had a lot of sketches in that vein. The most famous of those was one where a pair talked about third person and their naïveté (or about some naive act they committed themselves), and when they were to say "because I/you/he/she/them are such a..." they were always interrupted by a bag salesman crying "Bolsa!". (In Venezuela, "bolsa", besides his "bag" meaning, is also an euphemism for "idiot" or "naively dumb").
 * A similar sketch has people discussing someone's hotness and what they intended to do with that person, when they were interrupted by a machete-bearing country salesman crying "¡Machete!", who was covering his groin. ("Darle machete" is a somewhat rude way of saying Intercourse with You).
 * Often inverted hilariously on the "Whose Line" sketch of Whose Line Is It Anyway, a game where performers have to perform a skit and, at various times, pull out some lines previously written by the audience and use them as if they were what they had been about to say. Much of the humour in this game involves totally storyline-inappropriate lines being pulled out, and the performers trying to segue them in with the rest of the performance. In this game, for example, Ryan Stiles had to say he was dressed as a French maid during Davy Crockett's last stand at the Alamo due to one of the pre-written lines.
 * This entire A Bit of Fry and Laurie sketch.
 * One episode of Monk, "Mr. Monk and the Miracle", features this in a scene where Monk and Natalie find Randy at the police station. It works because Randy has his back to them when the scene begins:

"[Monk and Natalie are following Marilyn's movements] Adrian Monk: God, I can't wait to see his face! Natalie Teeger: Mr. Monk... [sees Monk pull out a very old camera] ...what is that? Is that your camera? Where did you get that? Adrian Monk: It's a birthday gift. Natalie Teeger: From who? Thomas Edison?"
 * This is also the case in one scene in "Mr. Monk and the Bully", in season 7:

"Amy: When she walks, she's like a samba that swings so cool and sways so gentle that when she passes, each one she passes goes..." Sheldon: (knock, knock, knock) Amy? (Knock, knock, knock) Amy? (Knock, knock, knock) Amy?"
 * In the second Season 5 episode of The Big Bang Theory, Amy Farrah Fowler is playing the harp and singing "The Girl From Ipanema" when Sheldon pays her a visit.

"Sheldon: (knock, knock, knock)... Penny: WHO DO WE LOVE? Sheldon: ...Penny?"
 * Another episode in Season 5 has Penny invoking this trope when Sheldon knocks on her door in his usual manner:


 * The Mastermind sketch by The Two Ronnies where the contestant answers the question before last.
 * Frasier: "No one's going to sell me on anything. Those exercises only helps people who lack self-awareness. I, for one, am...[winces in pain] God Almighty!" (Niles responds with "Well, no wonder you're stressed; you've got a whole universe to run!")

Theater

 * Noises Off: At one point, a character quietly moving about backstage inadvertently shouts, "OH MY GOD!"... precisely on cue.

Western Animation
"Lisa: But perhaps most dangerous of all is the ] SCORPIONS!"
 * In The Simpsons episode "The Scorpion's Tale", Lisa is wandering through the desert reading a book about the dangerous wildlife, ending with (paraphrased)

"Teacher: And then George Washington said (Jane walks in) young lady you're tardy."
 * In an episode of Family Guy, a Wall Street trader is on the phone to his company relaying some important information about the state of the stock market and is hit on the head by a stray golf ball causing him to say: "...so be sure to buy lots of [blow to the head] Waffles! Tasty waffles with lots of syrup!" Cue a scene of Wall Street traders shouting "waffles!" and then, oddly, Japanese traders going crazy screaming "Waffur!".
 * Happened in Daria:

Web Original
"Interviewer: Why don't you tell me a little bit about why you'd like to be a substitute teacher? Ian: Well, I really really love...BALLS!"
 * Subverted in this Smosh epsiode.