Perhaps this can be forgiven in such a whimsical comedy, but whenever M. Arpel parks his car in his tiny home garage, he always pulls in front-end first; however, whenever he leaves for work in the morning, the car always exits the garage front-end first. (Possibly a subtle sight gag on Tati's part?)
When the boys are playing their traffic prank, one of their victims steps out of a 1955 Pontiac Chieftain. In the next cut, as he goes to argue with the woman he thinks has rear-ended him, the Pontiac is replaced by the 1951 Oldsmobile 88 driven by Charles Arpel near the start of the film (and which he is still driving at this point). Even the license plate (523 AP 75) is the same.