You are walking alone down the street. Suddenly, you hear footsteps (脚步声). Is someone following you? How do you know the footsteps are someone else’s and not your own?

You can tell because your brain (大脑) has the ability to ignore (忽略) certain sounds, according to a study from New York University in the US. Because of this, we often ignore our own footsteps. But we may easily hear others’ footsteps.

Scientists tested this on mice. They found that when mice became familiar (熟悉) with the sound of their own footsteps, they developed a “sensory filter (感觉过滤器)”, according to David Schneider, one of the lead authors of the study. This allowed the mice to ignore the sounds of their own footsteps. They could more easily notice the sounds of their environment.

“For mice, this is really important.” Schneider told Science Daily. “They need to listen to a cat getting close to them, even when they’re walking and making noise.”

Our brains don’t just ignore our footsteps. We also ignore some other sounds that we make ourselves, including the sound of eating, breathing heavily and typing on a keyboard. Being able to ignore these unimportant noises lets us pay attention to more important and dangerous ones. For example, we are quick to notice the sound of a baby crying. So we can rush to make sure they are okay and keep them alive. The same idea applies to humans screaming. When we hear this sound, we can quickly go to help the screaming person.

The AI (人工智能) has changed our lives. There are four useful AI inventions here.

Many people have the wrong ideas about pigs. Pigs are actually（实际上） very clean animals. On the farm, they live in dirty places, so they become very dirty. But in the wild, pigs keep themselves very clean. They are also very smart. They may be smarter than dogs. So pigs can learn things from people.

Pigs are very friendly animals. Some people raise（饲养）them as pets. Of course, people raise the small kind, not the big kind. Small pigs are very cute. And they don’t break things in the house. Big pigs usually live outside on the farm, not in people’s homes.