Below is a selection from a popular science book. If blood is red，why are veins（静

If blood is red，why are veins（静脉） blue？

Actually，veins are not blue at all. They are more of a clear，yellowish colour. Although blood looks red when it's outside the body，when it's sitting in a vein near the surface of the skin，it's more of a dark reddish purple colour. At the right depth，these blood­filled veins reflect less red light than the surrounding skin，making them look blue by comparison.

Which works harder，your heart or your brain？

That kind of depends on whether you're busy thinking or busy exercising. Your heart works up to three times harder during exercise，and shifts enough blood over a lifetime to fill a supertanker. But in the long run，your brain probably tips it，because even when you're sitting still your brain is using twice as much energy as your heart，and it takes four to five times as much blood to feed it.

Why does spinning make you dizzy（眩晕的）？

Because your brain gets confused between what you're seeing and what you're feeling. The brain senses that you're spinning using special gravity­and­motion­sensing organs in your inner ear，which work together with your eyes to keep your vision and balance stable. But when you suddenly stop spinning the system goes out of control，and your brain thinks you're moving while you're not！

Where do feelings and emotions come from？

Mostly from an ancient part of the brain called the limbic system. All mammals have this brain area — from mice to dogs，cats，and humans. So all mammals feel basic emotions like fear，pain and pleasure. But since human feelings also involve other，newer bits of the brain，we feel more complex emotions than any other animal on the planet.