clam up
中上級 (B2) informal
To suddenly become very quiet and refuse to say anything, like you've closed your mouth tightly and won't open it
"Every time I try to ask him what's wrong, he just clams up and leaves the room."
To suddenly become very quiet and refuse to say anything, like you've closed your mouth tightly and won't open it
"Every time I try to ask him what's wrong, he just clams up and leaves the room."