shut up like a clam

to suddenly stop talking and to refuse to say any more

Usage notes: A clam is a fish with a shell which closes up very quickly if something attacks it.

When I asked him about his trip to Korea, he shut up like a clam.

Name	Pronounced	Usage
Varpu	VAHR-poo	Finnish
Paola	POW-lah (Italian), pah-O-lah (Spanish)	Italian, Spanish
Vosgi	-	Armenian
Desiderata	-	Late Roman
Isis	IE-sis (English)	Egyptian Mythology (Hellenized)
Sequoia	sə-KOI-ə	English (Rare)