Another trickey joke question.Will never get right.?

2 boys are playing in a shed.A ceiling fan falls and makes dust fly everywhere.1 boy is completely clean,and the other is covered with dirt.The clean boy rushes and washes his face and the dirty boy just sits there.Why did they do that?

The dirty boy saw the clean boy and thought he was clean too. The clean boy saw the dirty boy and thought he was dirty too.

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