Fly Subtraction Doubled
"If there were four flies on a table and I killed one, how many would be left?" asked the teacher.
"One," answered the bright little girl--"the dead one."
"Now, Johnny," said the teacher, "if there were eleven sheep in a field and six jumped the fence, how many would there be left?"
"None," replied Johnny.
"Why, yes there would," said the teacher.
"No, ma'am, there wouldn't," persisted Johnny. "You may know arithmetic, but you don't know sheep."
Source: J. Braude's Handbook of Humor for All Occasions, 1958, p. 25, 133