After Max (Nathan Lane) and Leo (Matthew Broderick) do Der Guten Tag Hop Clop with Franz (Will Ferrell), Max tries to pull open the door. When it doesn't open, he shouts, "We're trapped!" This is an inside joke from the play's run in England. One night, a stage hand had locked the door. When Nathan Lane tried it, he realized it was locked and shouted out, "We're trapped! Trapped like rats with a crazy Nazi!" A stage hand then went up and unlocked the door and they got out.
A lot of the extras in the audience scenes were not actors. They're people who donated money through a charity and as part of their donation, they got to be extras in the movie.
Matthew Broderick wore an earplug in one ear where Nathan Lane yells "Never put your own money in the show!" up close.
The respective Hollywood Walk of Fame stars of Matthew Broderick and Nathan Lane are right next to each other.
Thomas Meehan: Max Bialystock's lawyer is played by the screenwriter of the film who was also the book writer of the musical.