What is the missing number?

One day a teacher had a taste test with her students. She picked a little boy to do the first test. She blindfolded him, put a Hershey kiss in his mouth and asked, "Do you know what it is?
"No, I don't," said the little boy
"Okay, I'll give you a clue. It's the thing your daddy wants from your Mom before he goes to work."
Suddenly, a little girl at the back of the room yelled, "Spit it out! It's a piece of ass!"