expression, godan verb (-su)
look displeased; flare one's nostrils
Idiomatic expression describing a facial expression of displeasure or sulkiness, literally 'to puff out the sides of one's nose'. Often used when someone is sulking or showing annoyance.
彼は注意されて小鼻を膨らませた。
He flared his nostrils in displeasure when he was scolded.
妹はおもちゃを取られて小鼻を膨らましている。
My little sister is sulking with her nostrils flared after her toy was taken away.