What joke is funny?

A man got a strange disease, so he went to the hospital to see a doctor.

The doctor asked, "What's the matter with you?"

The patient said, "I eat sausages and pull sausages." Eat bananas and pull bananas. In short, pull whatever you eat! "

The doctor said, "Oh, that's it. It's too simple. "

The patient said, "Oh, great. Then what should I eat? "

The doctor said, "Go eat shit and shit after eating!" " "