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Scientists think they have found the rat equivalent of a smile

Scientists have determined that rats seem to enjoy having their belly tickled. She lets out a sound too high-pitched for the human ear to detect and keep coming back for more.

Now, to add to the idea that rats have their own version of a smile, researchers at the University of Bern in Switzerland report in the journal PLOS ONE, that they have also been found in the rat-equivalent of a smile: lowered ears that are very bright.

They call it “face, indicators of positive emotions”, because, although it remains unclear whether rats are actually the feeling of happiness—the pink ears, for example, can only be the result of an increased blood flow as a result of physical effort—they seem to exhibit a positive reaction from their back for more.

“Although it is likely that animals do feel emotions, it is unknown whether they feel that they are in the same way that we do,” a researcher tells National Geographic, which reports that rats can be “literally tickled pink’, and that their ears hang down because their ear muscles to relax.

The researcher calls himself a “rat-tickling master,” and says that he found that rats respond to tickling differently; the shy and anxious, for example, prefer less stringent tickling.

Researchers have investigated negative emotions in rats (a “grimace” scale for measurement of pain) in an effort to inflict less suffering when it is possible, but this is one of the first studies that attempts to pick out a lab rat of positive emotions.

(The ability to excite themselves appears linked to schizophrenia-like properties.)

This article originally appeared on Newser: You Can Tell a Rat Is Happy with His Ears

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