expression, godan verb (-ru)
wag one's tail
Literal physical action of an animal moving its tail back and forth.
犬が嬉しそうに尻尾を振っている。
The dog is wagging its tail happily.
Idiomatic use likening insincere flattery to a dog wagging its tail to please someone.
彼は上司に尻尾を振ってばかりいる。
He's always buttering up his boss.