Scientists have long known that humans can hear an alarming squeak when rats fight, are in pain or something else is bothering them. At the same time, most squeaks have frequencies well beyond the human hearing range of 17 kilohertz. In previous tests, microphones caught squeaks in groups of rats, but experts could not identify the cause of the sound or the individual making it.
In their study published in Cell Reports, researchers from Israel’s University of Haifa said they had invented a tiny microphone that was attached to rats’ noses through a tube. The animals were placed in cages with ‘clean’ rats so that they were free to interact with each other, and recorded the sounds they made.
The experiment conducted by the researchers showed that rats made happy squeaks when they were in physical contact with another rat or when there was free communication. Moreover, according to the scientists, the squeaks were random rather than a response to any actions, as though the rats were just expressing positive emotions about being in the company of another rat.
The experts think that these squeaks are not a language, but a way of expressing joy.