In the first study of its kind, researchers at the University of Chicago show that rats engage in empathy-driven behavior, helping to free a trapped cagemate for no reward other than relieving its fellow rat’s distress. Rats chose to help each other out of traps, even when a stash of delicious chocolate chips was on the line.

Although previous research has suggested that empathy isn’t just the province of humans, this is the first study to show such pro-social behavior in rodents. Researchers say the basic understanding of empathy in lower animals could help scientists’ understand it better, and even increase it in people. “It’s a neat new experimental procedure that may facilitate the empirical understanding of empathy,” says Jaak Panksepp, a pioneer in the study of emotions in animals, who wrote a commentary that appeared alongside the new research in the journal Science.

In the rat experiments, researchers observed that the free rats immediately liberated their trapped partners, once they figured out how to open the restraint — which took about a week. Rats that were exposed to empty restrainers or a trapped toy rat ignored them.

“They are very smart and figure out if they pitch their nose up, they can open the door,” says Decety. “It’s not easy and it doesn’t happen by chance. They try hard and circle around.” The researchers did not teach the rats how to nudge the door open or give them any incentive to. Even when opening the door would release its companion into a separate compartment, rats freed each other.

Read the complete story on the Time website.