Jokes for all occasions: optical illusion

The sergeant rebuked the private angrily:

“Jenkins, why haven’t you shaved this morning?”

“Why, ain’t I shaved?” the private exclaimed, apparently greatly surprised.

“No, you ain’t,” the sergeant snapped. “And I want to know the reason why.”

“Well, now, I guess it must be this way,” Jenkins suggested. “There was a dozen of us usin’ the same bit of lookin’ glass, an’ I swan I must have shaved somebody else.”