adverb
with a twitch; with a jerk; with a flutter
Describes a small, sudden, involuntary movement, often of a body part like an eyebrow, finger, or corner of the mouth. Mimetic adverb.
彼のまぶたがピクッと動いた。
His eyelid twitched.
口元がピクッと引きつった。
The corner of her mouth twitched.