Mason placed rats in a Plexiglass pen with two cages: in one was another rat, in the other was a pile of five milk chocolate chips—a favorite snack of these particular rodents. The unrestricted rats could easily have eaten the chocolate themselves before freeing their peers or been so distracted by the sweets that they would neglect their imprisoned friends. Instead, most of the rats opened both cages and shared in the chocolate chip feast.
"In our lab we called it the 'chocolate versus pal' experiment," Mason says. "The rat could have put his butt in the opening of the cage containing chocolate to block the other guy, but he didn't. They were sharing food with their pals. In rat land, that is big—I was shocked." Mason says that free rats typically took the chocolate out of the cage before eating it and that sometimes the free rats placed the chocolate chips in front of or very near their recently sprung peers, "as if delivering it."
- Scientific American
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