TEACHER AND HIS STUDENT

A teache gave his student a class work to draw a cow eating glass,every student submitted their drawing but a
student gave his teacher a
blank piece of paper.
Teacher: What is this?
Student: It's a drawing of a cow
eating grass.
Teacher: (looked at the paper)
Where's the grass?
Student: The cow ate all of it.
, Teacher: (looked at the paper
again)Then, where's the cow?
Student: It left because there
was no more grass.