Metafictional Device

Normally, it would just be Paratext, or a basic building block of the fiction. But somehow, something used to construct the work -- the font of the text, or the formatting, a cute yellow thought/narration box or a dialogue balloon, quirks of spelling, the edge of the filmstrip -- is incorporated into the text, where the characters can interact with it. When this happens, that item becomes a Metafictional Device. Sometimes this involves Breaking the Fourth Wall; other times, it doesn't occur to anyone to wonder why that pretty thought balloon is visible, and it becomes more of a Strange Loop or Painting the Fourth Wall.

Ninja Prop is combining that with Chekhov's Gun.

Sorry I Left the BGM On, Panel Break and Harsh Word Impact are related to this.

"[Narration]: Do I still think in those little yellow boxes?
 * In Order of the Stick Lien, a paladin, discovers that a person is obviously evil, because he has a distinctive speech pattern; i.e., the dialogue balloon is black and the text is red.
 * Happens at least twice in There She Is In episode 1 Nabi doesn't understand why Doki is looking at him so intently, until he sees the heart symbols emanating from her, and is horrified (why? Watch the animation). Love hearts in their world also have physical (and sometimes painful) presence. In Episode 2 Doki's thought bubble is pushed out of the way by a friend as she comes into shot.
 * Deadpool:

Deadpool: "I'm good."

[Narration]: Ooh, I missed you, little yellow boxes! What fun we shall have together!"


 * Thursday Next: The footnoterphone, and a number of other things.
 * In the webcomic Sword And Sarcasm, it's common knowledge that mysterious invisible beings called the Choral Djinn secretly chronicle all the events of our lives. Part of Herbert's curse is that he and anyone standing near him can hear them. That is, they can hear the comic's caption boxes.
 * A great gag in one of the Chuck Jones-directed Tom and Jerry cartoons involves question marks and exclamation points appearing above the characters' heads... which they then grab hold of and use in their fight.
 * Whenever one of the characters on Sesame Street happens to notice the words, letters, and numbers materializing above his head while he talks.
 * In One Over Zero, Ghanny at one point contemplates whether they could use the contents of their speech balloons as tools or weapons. Junior is all in favor of the weapons part, but Tailsteak discourages the idea.
 * Used again when they're wondering about Tailsteak's nationality, noting he must not be American because Ghanny said "colour", with a u.
 * In this ''Cyanide and Happiness' strip, the characters are aware of the limited number of panels and necessity of a punchline.
 * One scene in Mahou Sensei Negima features a speech bubble impaling Chisame.
 * Yakko once gets an Idea Bulb, but Wakko eats it, leaving him without an idea.
 * In all of the Metal Gear games; if an enemy soldier discoveres where you are, an exclamation point appears over their head for a quick instant. In some of the games, if you shoot the exclamation point, it knocks them out.
 * The Tank Mc Namara strips for the week of July 12-17, 2010 show a pitcher who is able to read the thought balloons of the batter at the plate. The batter is concerned about being traded to another team as the baseball trading deadline approaches. Based on the batter's concerns that he can read, the pitcher, whose team is leading by 8 runs late in the game, "grooves" one to the batter to allow him to get a home run. In the Saturday strip, the catcher comes out to the mound. The pitcher assumes that he's in trouble for allowing the home run and begins his explanation with how he's heard the batter was about to be traded. The catcher then tells the pitcher how freaked out he is because HE was able to read the batter's thought balloons.
 * Oddly enough, no one says anything about being able to read the pitcher's thought balloons.
 * In the webcomic Keychain of Creation, the Crazy Awesome space, time, and fate-bending abilities of the Sidereal Exalted are represented by having them actively use the comic format against their enemies. In particular, Nemen Yi leaps between comic panels, abuses perspective to hit people at range with a melee attack (think "I crush your head", except it works), and breaks off a piece of the gutter (the border between panels) to use it as a throwing weapon.
 * In the video game Comix Zone, Sketch, trapped in his own comic book, can tear out part of the pages to use them as a paper airplane One Hit KO.
 * A few episodes of the Pokémon anime had Team Rocket interacting with the split screen; one time Jessie grabbed it and started hitting James with it.
 * There is the vine/root border in the Such Stuff Dreams are Made On arc of the Mega Crossover fancomic Roommates which is a flourish indicating "dreams". Until it attacks that is.