In the episode where Frasier, Niles, Marty and Dafne go to Canada in the motor home, Marty reads a road sign which says: "Have your picture taken with a live bear, 1 mile". Problem is, they were in Canada (we know this because we're in the car for the whole mile and they never cross the border) and in Canada the Metric system is used as opposed to the Imperial, which means the distance should be in kilometers rather than miles.