to clam up 拒绝开口（俚语）

英文释义

To stop talking further; to become silent and uncooperative.

例句

I tried to determine who had created the problem at work, but when I asked the staff, they all clamed up because they wanted to protect each other.

我想确定是谁在工作中制造的问题，但当我问员工时，他们都不肯说，想互相保护。