When Christina Aguilera waltzes onto the field at Cowboys Stadium this Sunday, those attending Super Bowl XLV will rise out of their seats, remove their hats and listen to her belt out the national anthem with a certain patriotic zeal that’s otherwise reserved only for the Fourth of July.

Those at home probably won’t stand, but they will listen on their TVs or perhaps hustle into the kitchen to snag a frosty beer and a second helping of wings before kickoff.

Then there are those scattered around the world who will fervently hang on every syllable Aguilera sings -- some pleading with her to spit it out already and some wishing she’d take more time -- while simultaneously engaging the clock in a staring contest. As the seconds tick off, their hearts tick faster.

Welcome to the world of Super Bowl prop betting.

Prop bets allow you to wager on more than just the point spread and over/under. Bookmakers nowadays take prop bets on almost anything they can study and quantify, including an over/under of 1 minute, 50 seconds on Aguilera's rendition of the anthem.

As most of the stories go, prop bets appeared in the early 1980s, when Las Vegas casinos began hosting lavish Super Bowl parties for their big spenders. When a bet on the point spread seemed all but determined by the third quarter, interest in the game plummeted. To keep their guests entertained, casinos wanted to figure out a way to keep the high rollers betting until the game clock struck zero. They wanted bettors to feel invested despite the score.

Enter props. All of the sudden, it didn’t really matter if you weren’t going to cover the spread. Now there was a way for you to win that money back.

Prop bets didn’t gain traction nationally until Super Bowl XX. The Bears crushed the Patriots 46-10, but there was unprecedented buzz in Vegas. The week leading up to the game, casinos noticed that fans wanted to bet on whether William “Refrigerator” Perry would score a rushing touchdown. Chicago’s defensive lineman had scored two TDs that season, and many wondered if Bears coach Mike Ditka would dial his number on the goal line that Sunday.

He did.

Perry scored, Vegas wept and prop bets became a national sensation.

It was a sensation that needed to be tweaked, though, and that credit largely goes to Jay Kornegay, the bookmaker at the Las Vegas Hilton. Kornegay and his colleagues at the Hilton faced a conundrum in the 1990s when only two Super Bowls in that decade were decided by single digits.

The problem was clear: How do we keep bettors engaged during a boring game?

Before the 1995 Super Bowl, when the 49ers were favored by 18 points over the Chargers, the Hilton offered about 40 prop bets. To tempt bettors into laying money on a game that appeared to be as interesting as shoveling the remnants of a winter storm, the Hilton doubled its props.

The 49ers beat the Chargers by 23 points, and the number of prop bets has rapidly increased since then, with the Hilton offering more than 400 for this year’s game between the Pittsburgh Steelers and Green Bay Packers.

What are the coolest Super Bowl prop bets this year? Tune in Friday and find out.

-- Check out this year's most interesting Super Bowl prop bets