Want to see a rat laugh? Then tickle it. Dogs laugh, chimps laugh and so do rats.
But rats aren’t laughing at jokes.
They laugh when they’re playing, in the same way humans do, to show that they’re happy and to encourage bonding.
The rats that played more, laughed more and the ones that laughed more preferred to be around other rats that laughed.
This is evidence that human laughter has evolved from play vocalisation, a behaviour seen in many other mammals.
In humans, laughter has developed into an important emotional expression, used throughout many channels of communication.
Think of the ways we try to convey laughter in text-based media, like smileys and LOLs.