A man walks into a Doctors office and puts a note on the table in front of the Doctor. The note says: "I can't talk, help me! "
The Doctor thinks for a while and says to the man, "Put your penis on the table here." The man thinks this is a bit weird but does as he says.
The Doctor takes a rubber mallet and hits his penis with it as hard as he can. The man cries in great agony: "AAAAAAAAAAAAAAAAAAAAA….." and the Doctor says, "Good, come again tomorrow and we'll learn B!"