Little Johnny Chicken Joke

A teacher asks her class, "Kids, what do chickens give us?"
The students all reply, "Eggs!"
Pleased, the teacher says,  "Very good class! Now what does the pig give us?"
To which the students reply in unison, "Bacon!"
The teacher nods approval and then says, "Thats right! Now what does the big fat cow give us?"
The class falls silent until Little Johnny raises his hand and when the teacher calls on him he confidently says, "I know the answer teach, it's homework isn't it?"