rack your brains

UK (US rack your brain)

rack /ræk/ v. 变形、折磨;榨取

to think very hard

绞尽脑汁，搜肠刮肚

I've been racking my brains all day but I can't remember her name.

我搜肠刮肚想了一整天，却怎么也记不起她的名字来。

Don't think this job a piece of cake. You'll have to rack your brains once you start on it.

别以为这工作是易如反掌的事，你做了就知道它是很伤脑筋的。