貝かいになる

expression, godan verb (-ru)

clam up; keep one's mouth shut; say nothing

Idiomatic expression literally meaning 'to become a shellfish', used when someone suddenly stops talking or refuses to speak, often in a stubborn or guarded way.

• 彼かれは急きゅうに貝かいになって、何なにも話はなさなくなった。

  He suddenly clammed up and stopped saying anything.

• あの子こは怒おこるとすぐ貝かいになる。

  That kid clams up right away when he gets angry.