I start to think of naughty things I want to do to Angelina Jolie. My eyes drift down to her cleavage. My neurons spit out dopamine. The machine whirs. Hmm. No good can come of this.

The fMRI (short for functional magnetic resonance imaging) captures 3-D movies of your brain to chart where the blood is flowing. When you speak, blood flows to the language centers. When you blink your eyes, it flows to the eye-blinking centers.