An animated character can talk, cry, yell, scream, or whatever, but while his mouth may undergo any number of contortions, the point of his chin never moves, and the general shape of his face never changes.
It takes a lot of time, effort, and artistic skill to animate characters whose faces stretch and warp realistically when their mouths open and change shape. Therefore, as a cost- and labor-saving measure, most of today's animated characters in all but the highest-end productions (or, of late, in CGI animation) are constructed with static heads/faces and a series of mouths that can be overlaid on them.
This wasn't always true—the older cartoons had full facial warping with speech, for example—but with the general decline in American animation starting in the 1950s, such shortcuts became standard practice. The exception in a cartoon that otherwise does this exclusively is profile shots; these are (usually) animated with full-face movement because otherwise, it looks much stranger than the animators want.
For similar reasons, the number of shapes required to animate a character's Mouth Flaps is kept to a minimum—some studios get away with as few as three to six mouth shapes (closed straight line/smile, closed mouth, small open, medium open, large "O", and an optional "screaming" mouth).
In a similar vein, many Object Shows exploit the fact that objects have neither jaws nor necks, so their mouths can move freely without having to modify the overall body shape.
Super-Trope of Cheeky Mouth (the mouth mysteriously migrates to the visible cheek when the character is viewed in profile) and Synchro-Vox (replacing the animated character's mouth with that of its voice actor to reduce costs) as the animated face doesn't move along the live-action mouth.
Sub-Trope of Anatomy Anomaly. Compare Ring Around the Collar (still characters are easier to animate talking when the head and body are separated by neckwear). Contrast No Mouth.
Since this trope is so ubiquitous, please limit examples to exceptions in 2-D animation.
Examples:
- Rejected: Whenever the characters speak, it's just their mouths that move, which at times look like they are floating and detached from their bodies, not the rest of their faces or whatever.
- Reynard the Fox: While averted for animals with long snouts, such as the title fox, characters like the raccoons might see their chins become a nonentity when they talk.
- The Saga of Windwagon Smith: While this trope is generally averted, with each character's jaws being richly animated for comic effect from the get-go, there's a scene after Captain Smith arrives when a townsfolk chews on some tobacco, perplexed. The only thing moving up and down is his mustache, while his face remains unchanged.
- Animal Crossing: Most characters are animated this way when they talk. It's only their mouths that move, with the shape of the head remaining the same.
- Hexepta: Mayor Attack: None of the characters from Acquittal: Induction move their chins when they speak.
- The Lord of the Rings: The Return of the King (EA): In the majority of the in-game cutscenes, only the characters' mouths are animated, so their heads retain the same shape. The most jarring is the scene in which Gollum bites Frodo's finger for the ring.
- Professor Layton vs. Phoenix Wright: Ace Attorney: Layton-originating characters speak only with their mouths, despite the fact that the original and Ace Attorney characters do not.
- Acquittal: Induction: Only the characters' mouths move when they speak.
- Girl-chan in Paradise: Kenstar is one of the less animated characters, retaining the same arms-crossed pose with a fixed head shape that doesn't change when he opens his mouth.
- Wolf Song: The Movie: Roughly half the dialogue scenes are done like this, where, despite the cast all being wolves, their jaws aren’t animated when talking. The rest of the dialogue scenes, however, despite all being animated by the same person, are roughly evenly split between focusing on the eyes of the speaker (or the expression of the listener) and actually having the jaws move with the dialogue.
- The Amazing World of Gumball: Some of the characters are everyday objects/foodstuffs, such as bananas, slices of toast, balloons, potted plants, clay blobs, potatoes, peanuts, clouds, and ice cream cones. They are drawn in such a way that they don't have differentiated heads. Without that, they technically don't have chins, so unless their jaws drop to the floor in shock, their Mouth Flaps don't modify the shape of their heads/bodies. Now, there are characters that don't even have mouths, but that's another can of worms.
- The Animals of Farthing Wood: The human characters, rare instances we see them, have very static faces even as their mouths move. The only time we see any sort of chin contortion is when a man blows a hornet to start the hunt.
- Dastardly & Muttley in Their Flying Machines: While this is true for the frontal shots, Dastardly's chin goes up and down when he talks in profile shots.
- Dr. Katz, Professional Therapist: Surprisingly averted considering the rest of the animation is barebones. The characters might have their elbows and knees awkwardly animated but their faces will deform in funny ways when they speak.
- Fudêncio e Seus Amigos: Despite the show's Limited Animation, most of the characters' chins do move when they talk, and even the No Neck Chumps have a drawn chin on them that also moves. This goes in line with how the face is always animated with more detail (e.g., blinks and pupil movement).
- Hi Hi Puffy AmiYumi: Ami and Yumi's faces retain their shapes no matter whether the girls are screaming, singing, or even metaphorically getting slack-jawed.
- Kappa Mikey: Japanese characters, whenever they are not engaging in hammy moments, have essentially immobile faces whenever they speak, alongside very limited mouth flaps. Averted with Mikey who has the full lip spectrum and moving chin when speaking.
- The Simpsons: In one scene, Homer criticizes the quality of South Korean animation, and for the next few seconds, his mouth is detached from his face and floating in front of him.
- SpongeBob SquarePants: Due to most sea creatures (and invertebrates, in general) lacking what we call a neck, many of the show's characters have their faces near the upper end of their bodies. This means that when they open their mouths, they have no jaw that could move along either. Among the main cast, we have SpongeBob, Patrick, Mr. Krabs, and Plankton.
- Super Robot Monkey Team Hyperforce Go!: Unlike the robot monkeys, Chiro's face tends to retain its shape whenever he speaks or interjects.
- The Tales Of Waterville: Since the characters are animated Munchkees, their talking is depicted by black shapes flapping but no face or, well, body deformation coordinated, not even when they yell.
- Teen Titans Go!: Lampshaded by Starfire in "Classic Titans". When Control Freak forces the Titans to look like their 80s original designs, she points out that her chin no longer moves along her mouth.
- VeggieTales: The cast comprises vegetables only, and the vast majority are just a face slapped onto a veggie body. This means that they don't have jaws. Or if they do, it's not noticeable whether they move along when the characters talk.