Please do me a favor

A dentist, after completing work on a patient, came to him begging.

Dentist: Could you help me? Could you give out a few of your loudest, most painful screams?

Patient: Why? Docor, it wasn't all that bad this time.

Dentist: There are so many people in the waiting room right now, and I don't want to miss the four o'clock ball game.