The actor Alfred Then was a clown in real life. He even has an academic degree in it, but stepped out of the clown business shortly after the movie was completed. The reason for this decision was a personal one and had nothing to to with this film.
The opening sketch that the clown is showing to his audience is an adaption of a real life sketch done by Alfred Then in his clown career.
Originally the "Cart house builder" and the "whistling warden" were casted vice versa. But two weeks before filming the director decided to switch the roles; because Manfred Koller just looked more convincing as an in-patient. Both actors were happy with the decision.
All scenes outside the mental house were scheduled to be shot in two days. But rain came in, so the production was forced to stop filming. Due to schedule interferences with the cast, those two days became fife days spread over an entire month. This is also the reason for the bad weather continuity in the outside scenes.
The end when the little girl turns the "clown-nose" inside out wasn't planned in the script. It was an spontaneous idea, since the actress Kora didn't want to put on the clown-nose. A compromise was found by the director and her in turning it inside-out.