3 . You may have recently seen a video from the Beijing Wildlife Zoo becoming a hit. What exactly was so interesting about this video? It shows a dog playing with big cats four to five times its size! Many people might wonder if this dog has a death wish, but it seems that the dog and the big cats are good friends.

The dog was actually raised alongside the lion and tiger cubs, making up an odd but loving family, according to zoo officials. As opposed to the common belief, cross-species friendship has been around for centuries. People have domesticated many animals, most notably cats and dogs, and formed bonds with them as pets. Perhaps you even have a pet yourself.

There are many other instances of cross-species friendships.

At an animal sanctuary in Santiago, Chile, a jaguar named Marina and a deer named Laura formed a friendship after they both came to the park. As neither animal had a mother, sanctuary staff said they instantly bonded when they met. Laura had been rescued from a slaughterhouse while Marina had been rescued from the street.

One possible explanation for these friendships is the environment of the zoo. Animals don’t hunt for their food and don’t need to worry about marking their territory or looking for mates in the way an animal in the wild would. “All those activities take time and energy, and if these needs are removed, the animals get bored,” Gordon Burghardt, a psychologist at the University of Tenessee, US, told The Atlantic magazine. “In this particular situation, the animal’s motivation to engage socially and playfully may be higher in its need hierarchy(等级)than eating.”

Marc Bekoff, former biology professor at the University of Colorado, US, told Slate magazine, “I think the choices animals make in cross-species relationships are the same as they’d make in same-species relationships. Some dogs don’t like every other dog. Animals are very selective about the other individuals who they let into their lives.”

Belinda, like many of my students, had grown up "street smart", with very little use for schools and books. On the first day of school, she called Rory a very bad word, so I kept her in at break. I made her wash all the desks and pick up all the garbage lying around. "That'll teach her," I thought. Belinda, though, was smarter than me. "I like cleaning. Mr. Brassell," she said. "Can I do this every day?"

On the third day, I caught Belinda fighting with Jose. I walked over to their table and asked what the problem was. "She keeps calling me a bad word," Jose said. Belinda wrote standards after school while I gave her another lecture on behavior. The next day, I caught her fighting with Jose again. I shouted angrily across the room to ask why they were fighting. Again, Jose accused Belinda of calling him a bad word. Belinda had finally earned a home visit. I told her that I would walk her home after school and talk to her mother in person.

And for the first time all the week, Belinda became silent. For the rest of the day, she sat still in her chair, even with kids teasing her. "It's not going to work, young lady," I told her. "You already earned a walk home, and behaving now isn't going to change that."

When the final bell sounded, I took Belinda by the hand, and we began the two-block walk to her house. Belinda took me through the gate to her yard and she went inside to get her mother while I waited outside.

Where have you been, girl?" a voice screamed. Babies cried loudly inside.

"My teacher's here," Belinda said softly, and I still couldn't see inside through the front door.

"Hello," a deep voice barked. Then the door opened, and a rather skinny, short woman walked out.

"Uh, I'm Mr. Brassell, Belinda's teacher."

"What'd she done this time?"

I suddenly decided to try a different approach.

The next day at school, Belinda gave my knees a big hug.