The Octogenarian naturalist told fans of the terrifying sight during an hour-long Q&A session on Reddit
None so terrible, however, than watching monkeys brutally murdered by chimpanzees.
The Octogenarian naturalist, who released his latest film Natural History Museum Alive on New Year's Eve, was answering questions from fans during an hour-long Q&A session on social media site Reddit yesterday.
Asked by one member what he felt his distressing moment was, he said:
"Seeing chimpanzees kill monkeys, they do this to eat them.
"They chase them, set an ambush, catch them, and tear them apart," he added.
But, he went on to add, chimpanzees were also responsible for the most human act he'd witnessed in the wild: lying.
"Also, when some Colobus monkeys find a very precious piece of food, it calls the alarm call that it would make if a snake were to arrive, and all the other monkeys run away and it gets the food," he continued.
Perhaps even more distressing was his answer to whether he thinks the world is on the brink of a new era of mass extinction.
"Yes, I'm afraid we are," he wrote. "It's not possible to reverse the damage we've done. We are undoubtedly exterminating species at a speed which has never been known before."
"People should realise that waste of anything is something that we cannot afford in this overcrowded world," he went on to say, before praising the Worldwide Fund for Nature as an organisation everyone needs to know about.
In more trivial news, Attenborough said that his next project, a 3D film on the evolution of flight, is slated for release around Christmas this year.
His childhood inspiration was the naturalist Ernest Thompson Seton, and, most importantly, he revealed his favourite biscuit.
It's chocolate, if you must know.
"Seeing chimpanzees kill monkeys, they do this to eat them."