clam up phrasal verbphr v informalTALK TO somebody to suddenly stop talking, especially when you are nervous or shy 〔尤指因紧张、害羞而〕突然闭口，突然沉默不语 A sensitive child is likely just to clam up. 敏感的孩子可能就会闭口不言。
clam up• He always clams up when I ask him about his job -- do you think he's doing something illegal?• The police took her in for questioning, but she clammed up when they asked about her boyfriend.
→ clam up at clam2(1)