5 questions about your body you might not know the answers to

In fact, even scientists still don't know exactly why we yawn! There are several hypotheses, some of them being more scientifically backed. According to the theory about brain temperature regulation, we yawn to inhale extra air and cool down our brain. Another possible reason is that by yawing we try to wake our body up, stretching our lung tissues.

Why is yawning contagious?

Physiological theories state that seeing someone else yawn triggers the yawn reflex or simply makes us unconsciously imitate others' actions. According to the most popular psychological hypothesis, contagious yawning is all about empathy – we try to feel other people's emotions, and yawn too.

The are 3 types of tears:

• basal tears lubricate our eyes;
• reflex tears result from irritations, such as cold, gases or foreign bodies;
• emotional tears – crying or weeping.

As it turns out, tears caused by emotions have a chemical makeup different from other types of tears – they contain higher levels of stress hormones. Most likely, when we're feeling down, our body tries to literally get rid of stress through tears, which makes us cry. Anyway, these findings still need further scientific confirmation.

When our body temperature goes below normal, our brain sends signals to our muscles, telling them to tighten and loosen fast. When muscles move, they generate extra heat, helping us warm up.

Most commonly, laughter is considered a social expression. Our ancestors used this form of communication long before they had languages. Besides being a means of passing information, laughter is also good for us physically – when we laugh, our brain releases chemicals that make us feel better and more relaxed.

If you're enjoying this topic, try to ace this fun trivia quiz on human anatomy.

This natural movement doesn't need much effort from our arm muscles – it even helps us save energy while walking. Swinging arms offsets a part of the force caused by our legs hitting the ground, which keeps our torso stable and allows us to use less energy.

Bonus video: Why do we hiccup?