Expressions (phrases, clauses, etc.), Godan verb with 'mu' ending
a cornered rat will bite a cat; despair gives courage to a coward
Proverb
「そんなに舐められた相手じゃないけどなぁ・・・」「そうだよ、窮鼠猫を噛むって言うじゃないか」"I don't think she's an opponent you can ignore like that ..." "That's right, they say a cornered rat bites back, don't they?"
Also written 窮鼠猫をかむ【きゅうそねこをかむ】