The study was to see if a rat would help another rat with and without chocolate in another cage. What was discovered is that a greater number of female rats (6/6) as apposed to male rats (17/24) would open the doors of the trapped rats. They would then open the cage with the chocolate and share it with the liberated rat. The rats did not have a specific order in which they opened the cages but they would open both of them. Thus showing that the rats empathized and helped out their fellow cage mate.
The study write up and a video are links are below: