Why does sex make you sleepy?

Is the flipping of Earth's magnetic field a concern? Why might half-filled ice cube trays freeze faster? Why does sex make you sleepy? Why might you get an 'electric shock' from moving your head? Is nicotine addictive? Why does scratching an itch feel so good? Why do we have different blood groups? What are statins? Could we ever see the dark side of the moon? Dr Chris Smith and Clarence Ford have all the answers...