Shut up like a clam American British informal verb phrase
Used when one suddenly becomes quiet because one is nervous, upset, or does not want to mention a particular topic.
As soon as we mentioned the war in Afghanistan, the entire class shut up like a clam.
He shuts up like a clam when his father asks him about the result of his exam.
When I talked about his trip to Japan, he shut up like a clam.
Very quiet
It is so quiet that you would be able to hear even the tiniest sounds.
Extremely quiet.
Do something silently, secretly.
1. To keep silent.
2. To prevent someone from divulging information.
The verb "shut" should be conjugated according to its tense.