an onomatopoeic adverb meaning to start or flinch suddenly (a quick, startled movement).
物音がして、私は思わずビクッとした。
There was a noise and I involuntarily jumped.
先生に名前を呼ばれてビクッと振り向いた。
When the teacher called my name, I startled and turned around.
注射の針を見ると、子どもはビクッと体をすくめた。
Seeing the needle, the child flinched.
冗談で背中を叩かれてビクッとした。
I was tapped on the back as a joke and I jumped.