The Art teacher gives the students an assignment in class

The art teacher gives the students an assignment in class.

While inspecting she asked pappu, "what have you drawn?"

Pappu: that, ma'm - is a cow grazing.

Teacher: where is the grass?

Pappu: the cow has eaten it.

Teacher: but where is the cow?

Pappu: you don't suppose she'd be fool enough to stay there after she'd eaten all the grass, do you?