Other mistake: Richard Benjamin kicks in the door to the hotel room to shoot Yul Brynner, a.k.a. the gunslinger. When the gunslinger falls backwards out of the window his black hat never falls off, it stays on the whole time.
Other mistake: As the Governor looks at the gorilla sentries, he is looking about forty-five° across the aim of the cannon next to him. When the cannon is fired at the gorillas, they are directly downrange of the cannon. After they're killed, he's again looking across the cannon's aim.