[singular]a movement, action, or expression on someone's face that shows the truth about something or that lets you realize something that should be a secret 暗示的表情;暗示的举止
a dead (=obvious) giveaway (错误)明显的:
I knew she'd passed. Her face was a dead giveaway. 我知道她通过了,从她脸上的表情就能看出来。