also: にゅうっと · にょっと
adverb
suddenly appear; pop out; stick out abruptly
Mimetic adverb describing something suddenly protruding, extending, or appearing in a way that catches attention. にゅうっと is a slightly less abrupt variant.
猫が箱からにゅっと顔を出した。
The cat suddenly stuck its head out of the box.
ヘビが草むらからにゅうっと現れた。
A snake slowly emerged from the grass.
Mimetic word; the sound-symbolic combination にゅ suggests a smooth, sudden sliding or protruding motion. The exact origin is uncertain.