Why do we feel the need to laugh when someone else is laughing, even if we don’t know why?

Laughter is highly contagious due to the social bonding it creates. When you hear someone laugh, especially in a group, your brain’s mirror neurons light up, prompting you to laugh too. It’s an instinctual way of strengthening social ties, and it’s why laughter can spread through a room like wildfire, even if the joke isn’t that funny.