Rats laugh when they are tickled or play with each other.

Neuroscientist Jaak Panksepp discovered rat laughter in the late 1990s at Bowling Green State University. He used special microphones called bat detectors to hear the rats. These devices picked up sounds at 50 kilohertz. This frequency is much higher than the 20 kilohertz limit of human ears.Panksepp found that rats chirped most when they played or when he tickled their necks and bellies. The rats liked the tickling so much they would chase his hand to get more. This behavior shows that rats have social bonds and feel joy.Inside the rat's brain, tickling triggers the release of a chemical called dopamine. This happens in the nucleus accumbens, which is the brain's reward center. Humans use this same brain pathway when they feel happy. It proves that the rats are not just making noise but are experiencing a positive emotion.In 2016, researchers Ishiyama and Brecht published a study in the journal Science. They found specific brain cells in the somatosensory cortex that react to tickling. When they used electricity to trigger these cells, the rats laughed even without being touched. This confirmed that the chirps are a physical reaction to pleasure.