Revealing mistake: Blank firing adaptors are visible on the bow machine guns of Oddball's Shermans as they shoot up the rail yard. (01:00:05)
Revealing mistake: The cannons shown are firing blank charges, which produce no recoil. Recoil has been simulated by towing the guns backwards when they fire. The problem is, there is always a distinct delay between the discharge and the "recoil." The cannon also seem to largely fire explosive shells. At no point do we actually see a cannon ball rolling or bouncing along the ground or into any group of soldiers.
Revealing mistake: When Ursus is giving his speech in the Ape city, many of the Chimpanzees and Orang-utans are wearing incredibly fake-looking masks. (00:17:15 - 00:19:50)
Revealing mistake: When the guy who was stealing money from the lady's garter gets run over by the getaway car, it's obvious that the actor stops way before connecting with the corner of the car - and the trajectory of his bump afterwards does not make any physical sense. (00:15:15)