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."