The cherries, lemons, and plums on a slot machine were originally flavors of chewing gum, put on the reels to dodge early anti-gambling laws. This episode traces the machine from an 1893 Brooklyn device by Sittman and Pitt, which spun 50 playing cards on five drums and paid out in beer and cigars from the bartender, to Charles Fey’s three reel Liberty Bell in San Francisco, the first to pay coins automatically. When California banned the devices, makers disguised them as gum vending machines, and courts in Iowa saw through it.

The second half of the story is mathematical and psychological. Three physical reels could only offer about 1,000 outcomes, far too few for a life-changing jackpot, until electronics and a 1984 patent for the virtual reel cut the link between what a player sees and the real odds. From there the episode examines return to player percentages, the trance researchers call the machine zone, and why software glitches that show huge jackpots almost never get paid.

• Sittman and Pitt removed the ten of spades and the jack of hearts from the drums, halving a player’s chances of a royal flush.
• Bally’s 1963 Money Honey added a motorized hopper that could pay out up to 500 coins automatically, making the pull lever unnecessary.
• Inge Telnaes’s virtual reel mapped 256 digital stops onto 22 physical ones, creating over 16.7 million combinations across three reels.
• Mike Dixon’s research at the University of Waterloo found that losses disguised as wins trigger the same arousal as real wins.
• In 2010, two Colorado players saw jackpots of $11 million and $42 million displayed by a software bug, and the state ruled the casinos owed them nothing.