In different circumstances, gorillas can be truly dangerous.Most gorilla violence is directed towards other gorillas.
They live in groups, in which one dominant male silverback controls several females and youngsters. If another male approaches, the silverback will try to drive him off. He begins by making threatening displays such as grunting, hooting and chest pounding. If that does not work, he may attack.
Many silverbacks have tell-tale scars from such encounters. The losers sometimes do not survive.
Gorilla attacks on humans follow a similar pattern: the gorilla has to be provoked first.
Ian Redmond of Ape Alliance worked with Fossey in Rwanda for three years in the 1970s, and still works with gorillas. He says there have been cases where gorillas attacked and even killed humans, but such incidents are rare – and the human was always to blame.
"All the incidences I know where people have been hurt by gorillas, or in some cases killed by gorillas, are in the wild where the gorilla feared an attack or was actually attacked," says Redmond.