Charlie is attacked by monkeys on the tightrope (The Circus,1928)

In 1929, Chaplin told Czech journalist Egon Erwin Kisch some of the difficulties, physically and otherwise, he had filming this scene:

He also tells stories about his own films. The monkeys in Circus scratched him badly and for six weeks he had to be in a doctor's care. Even now he has two clearly visible wounds. 

Then there was the bellowing of the monkey's owners. The monkeys, you see, belonged to four different extras, each of whom regarded his own as the main attraction. "Turn the camera downward," one of them yells to the cameraman. "Can't you see that Johnny's on the ground?" Another: "Now, now! Mungo's face is turning this way." Charlie plays the scene: four monkeys, four tamers, himself, and the cameraman. (Egon Erwin Kisch, The Raging Reporter: A Bio-Anthology, Purdue, 1997)

Chaplin with the monkeys and their trainers.