Other mistake: When Harpo and Chico are shooting spitwads at Groucho in the classroom, Groucho's line gets cut short when he is hit flat on the side of the head with a book. He then falls back and says, "You got me" and if you listen closely you can hear someone laugh in the background.
Other mistake: In the opening credits, The Pharaoh (James Crane) is misspelled as "The Pharoh."