You'll be disappointed!

[funmonger]

Jane was sitting in anatomy class on day when her teacher asked her a question. He inquired, “What grows to 10 times its original size when excited?”
Jane blushed and said that she didn't know. Jimmy raised his hand and said, “I know! The pupil of the eye.” The teacher replied, “Yes, very good Jimmy.”
The the teacher turned to Jane and said, “Jane I have three things to say to you: One -- you have a very dirty mind. Two -- you haven't been studying hard enough. And three -- you're going to be very disappointed!”