This Silverback thinks this intruder in the mirror (his own reflection) comes to steal his wives

In the mirror each of these gorillas sees the reflections of its family members by its side, but it is also faced with one gorilla it has never seen before: its own reflection. Each gorilla attempts to get to known this never before seen gorilla who copies its every movement. As the gorilla approches the stranger, the stranger approches as well, when the gorilla tries to touch this newcomer, the newcomer also reaches out its hand but its fingers are met with a cold, flat surface rather than the warm touch the gorilla was expecting. When the gorilla tries to press its lips against the stranger or lick its face the result is the same, once again the gorilla encounters this cold, hard surface. Some of the gorillas reach behind the mirror in an attempt to touch the stranger without coming in contact with this flat surface.