Who can define the joke that cows eat grass or add something?

Joke ~ One day, the art teacher asked Xiaoming, "Where are your paintings?"

Xiaoming: "Teacher, this is one of my paintings!" " "

Teacher: "What are you drawing?"

Xiao Ming: "Teacher, I painted cows eating grass."

Teacher: "It's obviously a blank sheet of paper, and there is no painting?"

Xiao Ming: "Teacher, the grass was eaten by the cow, so there is no grass on the picture."

Xiao Ming: "Teacher, the cows left after eating the grass, so there are no cows in the picture." ...

De ...

food chain

It's amazing.