I've done one of those stunts, accidentally of course. Well, halfway did it - used to ride down this big hill in the woods behind Albright Cemetary near Kokomo. It had been raining for a couple days, path was all muddy (like an inch of wet mud on top of hard clay) and I couldn't stop in time to avoid a big tree that had fallen. Slid the bike sideways so both wheels hit the log flatways and I went flying off. Scraped my ankle pretty bad but was otherwise not seriously hurt.