it's almost as bad as that feeling of ripping down a fast whooped out section of single track and catching an angled root in the bottom of one that grabs your front wheel and shoots you off the trail towards a big ass pine tree, the moment your front wheel comes out of the whoop 25 degrees off your intended course you know your screwed. 
Oh man those are the worst... especially when the ground is a little wet...
Last year I was riding in the bush with a couple buddies, and I swapped bikes with one dude, took his 03 kx 125 out. I was hauling ass down a fairly smooth trail, just had some up and down flow to it... pinned in 5th gear and didnt see this root across the trail until the front wheel hit it. It was wet of course and I shot strait off into the trees. I was stopped instantly by a tree that hit me in the right shoulder/chest, and the bike kept going. It was mangled. lol buddy wasnt to impressed.
