Want to make an easy buck? Bet a friend that he can’t catch a dollar bill. Have your buddy make a lobster claw out of one hand and hold it out toward you, knuckles pointing to the side. Hold the bill lengthwise from the top between your friend’s fingers and thumb, with about half of the bill protruding above the claw before you let go. There’s only one rule—your friend may only close his hand once you drop the bill. If played fairly, this trick works every time. That’s because it takes a human longer to react than it takes for an object to fall 3 inches. Why are we so slow? Catching something is actually a pretty complicated maneuver: First your eyes must see the bill start to fall; then your brain must process this report and tell your motor neurons, “Close the hand”; and finally, your finger muscles must contract in a pinching motion. Really, getting all that done in about 0.18 seconds is pretty impressive. Reaction time comes down to the way our nervous systems are wired. It takes a certain amount of time for signals to travel from the sensory organs (eyes, skin, ears) to the brain, and a certain amount of time for instructions to travel from the brain to your muscles. If you can predict the appropriate response, you can decrease your reaction time, but only so much. And if you have to make a decision about how to react to a stimulus—like a goalie trying to block a shot—it takes longer to react than it would if you knew you just had to pinch your fingers together as soon as a bill starts to fall. But, as you now know, that takes long enough. Cha-ching!

Thanks to Peter Strick, Pitt neuro-guru, for teaching us how to get our brains to play tricks on us. For more kids' stuff, www.howscienceworks.pitt.edu.