Panmammalian

A team of neuroscientists at Humboldt University in Berlin spent several weeks playing hide-and-seek with rodents in a small room filled with boxes. Instead of treats as a reward, they were given attention in the form of friendly petting and tickles. The scientists were surprised to see the rats having so much fun that they actually jumped for joy and laughed – in ultrasonic inaudible giggles which were measurable. They seemed to truly enjoy the fun in finding their sneaky human companions and being caught by them, getting more and more clever in short periods of time.-- anon
* Eavesdrop on Ultrasonic Rat GigglesBy Lydia Chain, Catherine Caruso on November 10, 2016scientificamerican.com