When this movie premiered in East Germany, the sentence "The wall comes all around the estate to keep them out, and keep us in" caused a roar in the audience. It was omitted in subsequent screenings.
A group of actors, gymnasts, and circus performers trained eight hours a day for several months to play the apes. Stage 7 at Elstree was their workout gym with ramps, mock trees and limbs, and nets for falls.