How do planes fly upside down?

How do planes fly upside down? Why do sheep eat so much grass? What is outside of the universe? How does hypnotism work? What does anaesthetic do? Why don't the colour stripes in toothpaste mix? Why don't we keep primates as pets? What is the cold shiver? Dr Chris Smith and Clarence Ford have the answers... Like this podcast? Please help us by supporting the Naked Scientists