When Dennis is in Mr. WIlson's bathroom after his bath, pouring mouthwash in his nose spray, Dennis has toothpaste all over his chin and mouth. When they show Dennis from the side, it is gone. From the front it is there again. This happens several times in the shot.
The film was released as "Dennis" in the United Kingdom in order to avoid confusion with the British comic strip character, "Dennis the Menace."