On this day 30 years ago, the Chicago Bears were en route to a thorough thrashing of the New England Patriots in Super Bowl XX when William Perry, the 325-pound defensive tackle affectionately known as “The Fridge,” was called onto the field.

In the third quarter, Perry, who had previously been used as a decoy in the game, lined up as a fullback near the goal line. This time, Chicago quarterback Jim McMahon handed him the ball. The rest is legend. Perry crushed his way through the defense and scored an historic touchdown.

“That one registered 3.8,” shouted NBC broadcaster Dick Enberg, referencing the Richter scale.

Among the game’s nearly 50 million viewers were a small coterie of celebrants who had actually bet ahead of time that Perry, who occasionally moonlighted for offensive purposes, would score in the game.

As David McIntire chronicled in SBNation in 2013, some of them made real money:

As [Chicago coach Mike] Ditka publicly down-played Perry’s role, the odds soared to as high as 75 to 1, potentially earning bettors $750 in winnings for every ten dollars bet on Perry to score. Then the national media picked up the story, relishing another colorful hook associated with a team that had created their own music video mid-season. As the publicity flowed in to Las Vegas, so did money. By kick-off the odds dropped to 2 to 1.

And so the “prop bet” (or proposition bet) was truly born, enabling gamblers, casual or serious, to wager on all kinds of aspects of the game beyond the outcome.

The germ of the idea is largely credited to Sonny Reizner, the legendary Vegas bookmaker, who in the sweep of the “Dallas” furor of the early 1980s tried to book bets on who actually shot J.R. on the popular soap opera. He was ultimately forced to refund all the bets, but the gambit was widely mentioned in his 2002 obituaries. Just a few years later, Perry’s Super Bowl rumble opened the door for the dream of whimsical betting to flourish into a multi-million dollar venture.

With the line-up for Super Bowl 50 now set and the game less than two weeks away, a new slate of possibilities will soon open up.

“The props always draw good action,” MGM Resorts sports book director Jay Rood told The Las Vegas Review-Journal. “We're trying to come up with some new ones, and we're even going to put some props up at halftime on the fly.”

Some curiosities that will likely emerge as prop bets: How long will it take for the national anthem to be sung? What color Gatorade will be dumped over the winning coach? How many times will Broncos quarterback Peyton Manning shout “Omaha” during the game?

Unsurprisingly, whether the pre-game coin toss will yield heads or tails always draws even odds. Prior to last year’s game, the previous 48 Super Bowl coin flips delivered an even count of heads and tails with 24 each. Last year, the Seattle Seahawks won it when the coin landed on tails—so be sure to use your head.