It marks as the first time Brian De Palma got out of the independent cinema and went to work for a studio system, in this case Warner Bros. They fired him after disliking everything he shot. The event traumatized the director and it would take almost 20 years for De Palma to work again with the studio, and the movie was The Bonfire of the Vanities (1990).
Orson Welles didn't bother to learn his lines. A frustrated Brian De Palma insisted they reshoot every scene until Welles got his lines right.
The very first 20 second scene that begins the film (right after the Warner Bros. logo) involves Tom Smothers and John Astin carrying on a conversation while facing each other standing in front of some office doors. When they finish and part, one suddenly realizes that it's been a clever staged optical illusion - in that they were occupying two different spaces and were paired together via split screen.