An onomatopoeic adverb indicating a small, sudden twitch or jerk (a brief reflex or spasm).
犬が後ろ足をピクッと動かした。
The dog gave a little twitch of its hind leg.
彼は驚いてピクッと肩をすくめた。
He was startled and gave a quick shrug of his shoulders.
試験の結果が思ったより悪くて、顔の表情がピクッと変わった。
The test results were worse than expected, and his expression twitched for a moment.