The Bathtub Test

A psychiatrist was asked how they tell if someone is compus mentis.

"Well," said the psychiatrist,  "we fill up a bathtub, then we offer a  teaspoon, a teacup and a  bucket to the person and ask him or her to empty the  bathtub."  

"Oh, I understand," said  the visitor. "A normal person would use the bucket because it’s bigger than the spoon or the teacup."

"No." said the psychiatrist, “A normal person would pull the plug. Do you want a bed near the window?"