A police officer pulls over a car full of nuns and asks "Why were you driving so slowly?" The nun driver replies "The speed limit is 20 miles an hour, officer." "No, Sister, the speed limit is 70." "Then what are all the signs that say 20 on them?" "This is highway 20. They just mark what highway you are on." "Oh... That explains why the other sisters were screaming back when we were on Highway 166."