Meaning of 噛む in Japanese

「僕の歯はとっても弱くってりんごはかめません」と男の子は言いました。
"My teeth are too weak for apples," said the boy.

つめをかむ癖を止めなければ行けない。
You must get rid of the habit of biting your nails.

彼女は姑の気にさわるようなことを言わなければよかったと臍を噛んだ。
She bitterly regretted having said something that displeased her mother-in-law.

「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?"

どうも彼はその件に一枚かんでいるようだ。
It sounds to me as if he has something to do with the matter.