Clam up
Definition 1 of 1
Pro Tip 1/3Emotional Silence
Used when someone stops speaking due to strong emotions like fear, surprise, or sadness. 
When confronted about the theft, he clammed up from shame.
Pro Tip 2/3Pressure Response
Common reaction to being under scrutiny or intense questioning, not necessarily guilt. 
During the intense interview, the candidate clammed up.
Pro Tip 3/3Avoiding Details
May indicate someone is intentionally withholding information or avoiding a topic. 
She clammed up whenever the conversation turned to her past.