Why do eyebrows grow so slowly?

Have you ever wondered why eyebrows grow so slowly, or when you should brush your teeth in the morning? Can you tell the difference in sound between hot and cold water being poured? What causes those cold shivers down your spine? Is a spirit presence real? What controls how fast we move? Why do people mix oil with butter when cooking? And what's the best way to get vitamin D? Dr Chris Smith and Clarence Ford have the answers. Like this podcast? Please help us by supporting the Naked Scientists (thenakedscientists.com/donate)