Head Bob

"Sarge: What are they saying?

Simmons: I have no idea. I can't find the volume on this monitor. And without any sound it just looks like a bunch of helmets bobbing up and down.

Sarge: Is that how they talk? They look ridiculous!"

- Red vs. Blue

In any work where the character's mouth will never move, such as with Puppet Shows, masked characters, mouthless animation and Machinima, in order to simulate speech, the "puppeteer" will aim up and down in time with the dialogue. This produces a bobbing motion for the character's head. If a mid-1990s 3D Video Game went to a Cutscene, quite often it was stuck with this too (Metal Gear Solid was regarded as a technical breakthrough, but its characters didn't have eyes, let alone movable lips).

Probably the Trope Makers from Ancient times with an influence spreading to modern works are the old puppet shows. From Older Than Feudalism shadow puppets to post-Industrial Punch and Judy, the clearest and probably only way to denote who was speaking was by bobbing the head as they spoke in a different voice.

This is not just an Animation Trope. In some live-action TV, especially Sentai shows, the helmeted characters will exaggerate their head movements to suggest that they are actually speaking.

Compare Action Figure Speech, where the whole body moves.

Films -- Live Action

 * Darth Vader in Star Wars is also a head-bobbing, arm-waving example of this trope. Many actors in heavy makeup or costume will resort to exaggerated movement reminiscent of the theater in order to get their emoting across to the audience.
 * Doctor Doom in the disastrous Roger Corman-produced The Fantastic Four movie is an extreme example of this, even going so far as to draw numbers in the air with his fingers when he says them.
 * The apotheosis of this is a video transmission opening with "HELLO, Richards! Good to SEEEEEE you again!" Translation: "[Queen Elizabeth wave] Richards, good to [points directly at eyes] you again!" ("I mean, this guy is just a few short gestures away from inventing Latverian Sign Language.")
 * Averted in V for Vendetta. V gestures and moves around a lot while speaking, but he doesn't bob his head or do anything beyond the realms of the normal. Makes sense, since he's never in the same scene with anyone else in a mask.

Live Action TV

 * Suited Power Rangers use the Head Bob and exaggerated gesturing. In early seasons, it was sometimes accompanied by the air-whipping sounds typically reserved for fight scenes. Huh? What Do You Mean It's Not Awesome??
 * Though not to the titanic degree of Mighty Morphin Power Rangers, Toku in general (including Super Sentai, Kamen Rider, Metal Heroes, Ultraman, etc.) does this.
 * While it's true that there is some exaggeration to their movements, helmets worn by Power Rangers and Super Sentai actors are actually designed to move when the actor talks. Their chin pushes down on the bottom of the helmet and the whole thing shifts forward slightly giving the illusion of a Head Bob.

Puppet Shows

 * In The Sooty Show, with Hand Puppets that have no mouths, the main character Sooty is completely mute to the audience. He only communicates by "whispering" into others' ears and this whispering is designated by him bobbing his head up and down. His best friend, Sweep, who is similarly The Unintelligible and speaks only in high pitched squeeking noises, also bobs his head to stress the rise and fall of his speech. When he gets very excited or frightened the head bobbing get turned into rapid shaking to silly effect.

Theater

 * Ancient Greek actors wore wooden masks and conveyed emotion largely through dramatic gestures.

Video Games

 * In fact, the first Half-Life was one of the first games to avert this by having at least semi-realistic Mouth Flaps. Then in Half-Life 2, the aversion became even more spectacular as the technology used is actually capable of moving elements of the character's faces for realistic lip-syncing and expressions.
 * Since the leader of a given party in Guild Wars can be of any class and either gender, wearing any of the available armor sets, this is how in-game cutscenes are handled.
 * The first three Tomb Raider games always used gratuitous head bobbing to signify characters' speech. In FM Vs, the characters did not do this, but in some cases did not move their lips either, despite the fact that it was possible in this graphic engine.
 * In Okami, character's heads will stretch like putty every time any character talks, since people don't have mouths in the game's calligraphic art style. This is especially odd as there's no voice acting, just Banjo-Kazooie-style grunting.
 * Similar head-bobbing occurs during dialog in Neverwinter Nights. It's doubly strange because all parties will be bobbing at once (and only spoken dialog for key NPCs).
 * The original Metal Gear Solid on the first Play Station didn't provide for mouths, so this is how characters were shown to be talking.

Web Animation

 * Any Machinima done in an FPS, notably those done in Halo, like Red vs. Blue.
 * Note that when Sarge hangs a lampshade on it with the page quote, his own head movements are exaggerated.
 * A bug in the game Halo allowed a character to appear to be looking forward when in fact he was aiming at the ground. This allowed machinima artists to make it look like the characters had lowered their weapons. In Halo 2, this bug was fixed, but the game producers included a control to lower the character's weapon anyway.
 * Gothic allows one to make your character actually move their mouth and do gestures while doing it, but it's quite complicated, so the lazy machinima authors just bob heads.
 * The old Bionicle animations combined this with Noisy Robots.
 * Strong Bad from ''
 * In Homestar Runner'' bobs and waggles his head all over the place when reading e-mails, but in the earliest e-mails in which the viewer can actually see his lip flap (mask flap?), his head movement was much more subdued. The creators have admitted that they did this to save time, but now the effect takes about as much time as (or more than) just animating his mouth.
 * In one main page, as seen from behind the Main Page set, we see that Strong Bad bobs his head when not facing the viewer even when he thinks he's facing the viewer, and doesn't bob his head (much) when he is facing the viewer but thinks he isn't.
 * Coach Z also moves his head around when he speaks, because he lacks a mouth. Pom-Pom and the Cheat shake their entire bodies a bit when they... um, "speak".
 * And let's not forget Homestar's odd tendency to jerk his head backwards while talking. Of course, it does fit with his character...

Western Animation

 * While this is practically exclusive to the pilot (along with other anomalies), in the Five Episode Pilot of The Transformers, almost every time an Autobot or Decepticon speaks, they nod their head. Almost. Every. Time.