费神思考是指人在思考过程中，专注力很强，会感到疲倦或紧张。这个短语来自英语成语 "to rack one's brains"，意思是费尽心思，努力思考。

例句：

I've been racking my brains trying to come up with a solution to this problem. (我一直在费神思考如何解决这个问题。)
He was racking his brains trying to remember the name of the actor. (他费尽心思想起那个演员的名字。)
I can't seem to rack my brains for a good idea. (我似乎想不出好主意。)