where a rat was placed in water and another rat had the option to either pull a lever that saved the one in the water or pull a lever that released a chocolate treat. The rats pulled the lever to save the rat in distress, even though it meant forgoing the treat. When there was no other rat to save, they would just go for the lever that gave them the treat. Interestingly, if the rat with the choice of levers had been placed in the water previously and had gone through that experience, they were quicker to help the rat they had the chance to save.1
