According to Christopher Lloyd, after filming the scene where his character spears Gunther's apple with a knife and eats it, Hank Johnston, the young actor playing the role, was so frightened of Lloyd that he wouldn't approach him afterwards on the set.
During his first audition, Mason Gamble pulled a live worm out of his pocket. This inspired the casting directors to cast him.
Over 20,000 little boys auditioned for the titular role of Dennis Mitchell. Ten were selected to test the role with Walter Matthau.
During a Q&A in 2013, Christopher Lloyd stated that the scene where Switchblade Sam eats the beans, and jumps into the pond, was actually not in the original script.
Leslie Nielsen was offered the role of Mr. Wilson. He had to turn it down because he was committed to Surf Ninjas (1993).