Lip sync is matching a puppet’s mouth movement to speech so convincingly that an audience stops watching a hand and starts watching a character.
It is a performance skill, not a building skill, and it is learnable in an afternoon and refinable for a decade.
Open on vowels, close on consonants
Speech opens the mouth on open sounds and closes it on hard ones. A puppet that flaps continuously through a sentence reads as a machine. Say the line out loud, feel where your own jaw closes, and close there.
Drop the jaw, don’t lift the skull
The most common beginner error by an enormous margin. Opening the hand by raising the thumb tips the whole head back and the puppet appears to be gargling at the ceiling. The fingers stay level; the thumb drops. The eyeline never leaves the audience.
Hit the accent
One decisive open on the stressed syllable of a phrase does more than a dozen small flaps. Puppets are read at a distance, and clarity beats detail every time.
The body talks too
A head that moves while the body is dead looks like a head on a stick. A small lean into the emphasis, a settle at the end of the line — that is what sells it.
Match the energy
A shouted line needs a wide, fast mouth. A whisper needs almost nothing. Same jaw, different amplitude.
The hack: record thirty seconds of yourself talking, then practise to your own playback in a mirror. You already know exactly how those words should look, which makes every error obvious immediately.