small twigs and shit won't do much. your feet get pretty fucking tough. it's the big shit you gotta worry about. I shattered my heel once when I hit a water logged 2x4 floating in the water. I'm usually pretty good at spotting that stuff, but this was in a show and the guy outside of me was spraying the shit out of me. I never even saw it coming. Felt like someone lit off a stick of dynamite in my foot.
@ the OP - I can teach ya dude if you're ever in my neck of the woods. it's actually pretty easy to learn if you've got a boom (a boom is a bar that sticks off of the side of the boat...it may be in that vid....didn't watch it, but i think that vid is a clip from Mike Seipel's (sp?) Hot Rockin' Feet 2 in the 90's...I'm sure I've got that on VHS.) At any rate, the bar basically supports a lot of your weight so you don't get completely fucking owned when you're learning. I've taught a lot of my friends to foot this way before they even learned how to water ski.
The hard part is actually doing it long line. You will get rag dolled over and over again. And I will laugh my ass off every time. Don't take it personal...we've all been there....it's just that funny.