
Twitch
Involuntary Reaction
Twitch as a verb often refers to unintentional body movements, not something one does on purpose.

Whenever he hears a loud noise, his shoulders twitch.
Sudden Movement
A twitch is usually a quick, sharp motion that happens suddenly, without a gradual buildup.

The cat's ears would twitch at the slightest sound.
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ConvulseFlickerFlutterJerkQuiverSpasmTrembleWiggle
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