The Thanksgiving Day football game Mike and Sheldon discuss (where Mike wanted to shoot his TV and Sheldon's dad did) was the 1993 game between the Dallas Cowboys and the Miami Dolphins. In that game, which was played in a rare snowstorm in Dallas, the Dolphins squibbed their attempt at a game-winning field goal, leaving the ball spinning on the ground with members of the Cowboys surrounding it waiting for it to stop in order to declare it dead. However, Leon Lett ran up to try to grab it, but slipped and inadvertently batted the ball away, which made it a live ball again. The Dolphins recovered, tried the field goal again, and were successful, winning the game.
The legal definition of "want of understanding" is "the person did not know what a marriage was or understand what was going on" and is one of the most common reasons for annulling a marriage in the state of Nevada. This actually is appropriate for Penny and Zack, as neither one realized the marriage was real.
The mathematics that Leonard and Sheldon do in order to prove to Penny that cow tipping is impossible was previously done by the University of British Columbia. They reached the conclusion that one single person would never have enough strength to tip over a full-grown cow; depending on body type, it would take at least 2 to 4 people to muster enough force to do that, and then only if the cow doesn't adjust its footing or run away. Concerning the latter: cows don't sleep standing up (horses do that). A standing cow at night will be alert and hard to surprise, especially while being approached by 4 people. Even if it doesn't run away, it will shift its weight to prevent from falling over.
Contrary to popular belief, Jim Parsons did not improvise smacking Mayim Bialik on the backside. Bialik later said that although the smack wasn't in the original script, it was added a few days into rehearsals.