The water dumped on Caesar around 1:27:00 was supposed to be warm, but the crew forgot to heat it up. Caesar's shocked reaction is authentic. They were all apologetic afterward, but Andy Serkis said that it worked for the scene.
Primatologists who saw the film said the apes' behavior was surprisingly realistic. Karin Konoval's performance as Maurice the orangutan was especially noteworthy.
A shot of Bad Ape from behind, in a big, hooded winter coat, is the only time Steve Zahn appears onscreen without motion-capture gear.
While promoting La planète des singes : L'affrontement (2014), Andy Serkis was asked if the ALZ-113 drug had also affected apes outside of Caesar's tribe. Matt Reeves and Mark Bomback took note of it, which led to the introduction of "Bad Ape" in this film.
Matt Reeves pointed out that the apes in La planète des singes : Les origines (2011) and La planète des singes : L'affrontement (2014) don't wear clothing. The ape society seen in La Planète des singes (1968) wears clothing, and Bad Ape is also supposed to be the start of a progression in this direction. To survive in a harsh winter, he wears heavy winter coats he scavenged. This is primarily necessitated by the fact that he is bald, similarly to Rocket. However, while Rocket likely has Alopecia, Bad Ape seems to have lost his hair from old age.