On the other hand, these difficult vaults make for good TV. NBC did not show Canadian Brittany Rogers, because she didn't medal but also didn't crash. But we did see four or five replays of her teammate Ellie Black, who was doing a front handspring to one and a half flips and one and a half twists off.

Black is known for throwing impressive skills but with less impressive form. She didn't have enough height off the vault to land on her feet.

She got a zero for her first vault, because you have to land with your feet first before falling to get credit. She was smart not to do a second vault -- no point in risking further injury when she had no chance to win a medal.

While we are worried about Black's knees and other competitors' knees, we are actually worried for Yamilet Pena's life. All other competitors perform one-and-a-half flips off the vault. She does two-and-a-half front flips. That means if she's disastrously low or under-rotated, she could break her neck. Pena has only landed on her feet a few times in competition. That she had a kind of false start shows she knows how risky her vault is. This is worth 0.6 points more than the Amanar, and that's why she throws it, even though she rarely makes it.

It's possible that if she squeezed into a tighter ball and held on for longer, she could have stayed on her feet. But most gymnastics bloggers agree that she has poor technique, preventing her from getting enough power off the horse. Pena's strategy is to run up the score with difficulty points on her first vault, and then just land a relatively easy second vault, a double-twisting Yurchenko (one and a half flips, two twists). Her first attempt scored 14.566 and her second a 14.466, giving Pena an average of 14.516 and sixth place.

Russia's Maria Paseka did not fall, but we worry for her health, too. On her Amanar, she did more like two-and-a-quarter twists, instead of two and a half, and scored 15.4.

See this landing? Twisting into the mat like that is risking her ACL.

Her second, easier vault was much safer, but scored a lower 14.7. In the end Paeska averaged 15.083 and took home the bronze medal.

What makes McKayla Maroney special is that she is good enough to do her vaults easily and well. She goes higher than male gymnast Kohei Uchimura of Japan. Her legs are perfectly straight, her toes pointed. But last night, she was slightly off on her Amanar:

She drifted to the side and didn't get quite as much height as usual.

Compare that to team finals:

Of course, what is mediocre for Maroney — the 15.866 she scored made a gold medal all-but inevitable — would be amazing for her competitors. But NBC's commentators speculated that she was trying to go for a perfect stuck landing on her second vault to make up for the small deductions. And that's why she fell.

Even with the fall, she received a 14.3 — the score would have been a point higher without the fall — and gave her an average of 15.083 which was only good enough for silver. Others suggested she looked nervous, and that one arm looked weaker. Either way, if she'd made it as ugly in the air as her competition -- bent her knees to speed up her rotation -- she might have stood up. Instead, all Romania's Sandra Izbasa had to do was not fall.