Among orangutans, scratching is contagious – just as yawning is among humans. When an orangutan sees another scratch, they often start scratching themselves.
However, the behaviour differs from contagious yawning in one crucial respect. Humans catch yawns more readily from close family and friends, but the orangutans were more likely to catch scratching if they did not know the other orangutan well.
“I was doubting the results initially, but after checking everything it seemed to really be there,” says Daan Laméris at the University of Antwerp in Belgium.