Have you ever experienced the feeling of falling as you start to fall asleep? Sometimes you may come to realize this feeling. If so, don't worry. Many people have felt the same thing.

In fact, these muscle twitches (肌肉抽搐) in the arms, legs or other parts of the body are called hypnic jerks (入睡抽动) or sleep starts. And they are very common. Up to 70 percent of people experience them sometimes, Huffington Post reported. But what causes it?

There are some theories(理论). Some scientists believe that the feeling of falling comes from the body relaxing itself, especially if the person is anxious or unable to get comfortable. As you're about to sleep, your muscles become relaxed. But your brain stays awake. It misunderstands the relaxing of your muscles as a sign that you're falling. Then the brain jerks the body awake as if it's trying to protect you.

    Other scientists believe that different phases of sleep might cause the hypnic jerks. When we sleep, we experience two phases: non-rapid eye movement (NREM) and rapid eye movement (REM). During REM, our heart rate (心率), breathing and nervous system can act irregularly (不规律地). If the body experiences flashes (一瞬间) of REM while entering sleep, these irregularities could cause twitches.

If you don't want to experience hypnic jerks, scientists have some suggestions. When you become deeply relaxed, you can learn how to reconnect slowly by moving your fingers and toes a little bit. Then start to move your head and open your eyes, while being aware of yourself as you get out of the relaxed state.

    But experts agree that hypnic jerks, though sometimes scary, are harmless. If it wakes you up, simply roll over and go back to sleep. But keep in mind: a caffeinated (含咖啡因的) drink, exciting evening activities or stress may make hypnic jerks happen more often.

    How do you deal with plastic bags from the supermarket? Throw them away or recycle them? How about eating them?

    The bags are not harmful to the environment, Humans and animals can safely eat them. Indian company EnviGreen has made a bag with natural materials. It looks and feels just like plastic, but can break down(分解) easily.

    Ashwath Hedge who set up the EnviGreen Company spent four years doing experiments(实验) with 12 natural materials. They include potato, corn, vegetable oil and banana. He made the materials into liquid(液体) and used the liquid to make the bag.

    Although the EnviGreen bag is more expensive than a common plastic bag, it has many advantages. According to the Wall Street Journal, it takes 1,000 years for common plastic bags to break down. But an EnviGreen bag can naturally break down in less than 180 days. It also breaks down in less than a day in water, and in less than a minute in boiling water. Hedge was happy to show it in his interview, he put an EnviGreen bag in water and ate it with a smile.

    There are more than 15,000 tons of plastic waste in India every day. But only 9, 000 tons are processed. In China, 3 billion plastic bags are used every day. Maybe the EnviGreen bag could be a solution(解决方法) to the world problem of plastic pollution.

    Have you ever had the strange feeling that you were being watched? You tum around and, sure enough, someone was looking right at you!

Parapsychologists(R y3)say that humans have a natural ability to sense when someone is looking at them. To research whether such a "six sense" really exists, Robert Baker, a psychologist(心理学家) at the University of Kentucky, did two experiments.

    In the first one, Baker sat behind unknowing people in public places and stared at the backs of their heads for 5 to 15 minutes. The subjects(受试者)were eating, drinking, reading, studying, watching TV, or working at a computer. Baker made sure that the people could not tell that he was sitting behind them during those periods. Later when he questioned the subjects, almost all them said they had no sense that someone was staring at them.

    For the second experiment, Baker told the subjects that they would be stared at from time to time from behind in a laboratory setting. The people had to write down when they felt they being stared at and when they weren't. Baker found the subjects were no better at telling when they were stared at and when they weren't.

    Baker concludes that people do not have the ability to sense when they are being stared at. If people doubt the outcome of his two experiments, said Baker," I suggest they repeat the experiments and see for themselves