An adult hung clothes on a line. He dropped a clothes peg that he could not reach. Toddlers who were 18 months old helped. They helped a grown-up they had never met. Young chimpanzees helped a person who was reaching for something. They helped in easy tasks. They did not in the harder ones. Nobody asked or rewarded any of them for helping.

A free rat will open the door of a trap. It lets out a rat from its own cage. That rat is its cagemate. After some days of trying, rats opened the door with their heads. They did it fast. A rat was as likely to free its trapped cagemate first as to open a container of chocolate.

Vampire bats form strong bonds with their colony mates. Some unrelated bats have traveled together for more than ten years. A vampire bat can share some of its blood meal. It can share with another bat in its colony. A bat can starve if it misses a few nights of feeding in a row.

Asian elephants comfort other elephants. They do it when those elephants are upset. They use touch and sounds. An elephant may put its trunk in another elephant's mouth. This is to calm it. A researcher compared this to a handshake or hug.

Empathy is sensing and sharing what another person is feeling. A free rat acted more upset when its cagemate was trapped. It was as if it picked up the cagemate's distress. In a study, pet dogs went up to a crying person. They went to a crying stranger. Not only to their owner.

Words to know

• cagemate: cage companion
• distress: upset feeling
• toddlers: very young kids
• empathy: sharing feelings
• colony: bat group