His blood could boil. His lungs could overinflate. The vessels in his brain could burst. His eyes could hemorrhage.
And, yes, he could break his neck while jumping from a mind-boggling altitude of 23 miles.
But the risk of a gruesome death has never stopped "Fearless Felix" Baumgartner in all his years of skydiving and skyscraper leaping, and it's not about to now.
Watch his test jump below.