If you’ve ever considered becoming a pool shark in the vein of Minnesota Fats—or perhaps Tom Cruise in The Color of Money—you might have first considered how a nonsentient object like a pool table can tell the difference between the cue (white) ball and the 15 object balls in play. This is something most tables can do automatically, spitting the cue ball back out after a player sinks—or “scratches”—the ball by accidentally dropping it into a pocket.

You can tell small children it’s sorcery and they’ll probably believe it. But for older people, there’s a non-mystical explanation.

At coin-operated pool tables, players deposit money that allows the table to release the balls from a storage area under the playing surface. As players sink each ball, they return to the collection area until more money is inserted. When the cue ball is sunk, it doesn’t go to the same depository. A table can tell the difference in one of two ways: Either the cue ball is slightly larger—usually about 1/8-inch bigger in diameter than the standard 2.25-inch billiard ball—or it’s housing a magnetized center.

If the ball is oversized, it won’t be able to pass through the return chute and will instead be diverted to an accessible slot once it fails to clear a shunt that’s just a hair over 2.25 inches. If the ball is magnetized, a process first patented by pool table manufacturer Valley-Dynamo in 1966 will trigger a sensor that reroutes the ball along a track that will immediately spit it back out so players can continue. Some balls may instead be covered or dotted with metal so a magnet inside the table will pull it into position.

Both methods generally work well for casual play, but advanced hustlers might find fault with them. A larger ball can feel “off” to someone used to standard-sized cue balls, while the magnetized version can roll in subtle and different ways. Balls covered in metal are known as “mudballs” and are frowned upon for their slightly uneven surface. Better is the “cat’s eye” approach, which holds a steel bearing and closely resembles an unaltered ball.

Pro hustlers may steer clear of these doctored balls, but for your standard night out at a bar or family fun center, either one will do the job.

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