New research conducted in Switzerland and published in the scientific journal PLOS ONE found that rats display a wider range of emotions, including happiness, than scientists previously believed. A prior study established that rats enjoy being tickled, and perceive the activity as a form of play between themselves and humans. In this study, scientists selected the most ticklish 15 male Lister Hooded rats from a group of 75, and observed their appearance after a play period and a mildly aversive activity, in order to determine the contrast of their emotions. After the play period, the ears of all of the rats were more pink in color and less angular in position, indicating a state of happiness. Researcher Luca Melotti says that these findings have important ramifications when it comes to rats being used as test subjects in laboratories. “Not all regulations in every country are considering animals, especially lab animals, as sentient beings,” Melotti says. “So showing that … a wide range of emotions are measurable in those animals is very important.” Similar research was conducted with pigs last month, where scientists found that the animals have distinct personalities and can make pessimistic and optimistic decisions.