Scientists discovered that orangutan's laughter is infectious (to other orangutans, that is). And that evolutionarily, this may be a precursor to human emotions:
Orang-utans can also make each other chuckle – in fact, they are now thought to have developed laughter before us.
Our close biological cousins have a sense of empathy and mimicry which is an essential part of laughter, scientists at Portsmouth University discovered.
When one orang-utan displayed an open, gaping mouth – the equivalent of laughter – its playmate displayed the same expression less than half a second later, suggesting the mimicry was an involuntary display, their research showed.