While riding on our local Rails to Trails gravel paths, two riders passed my wife and I on cyclocross bikes. My wife and I, both on Fuji cross bikes kept pace with them and out of the blue this guy's rear wheel lifts up 3-4 feet and over he goes.
He said a bee went down his jersey and he reacted by jamming on the front brake. The bike was a Redline with a disc brake on the front wheel.
I was suprised how the wheel locked up and threw him over. And figuring the guy was 5' 8" 175, everything had to be just right to go over. It was as if the bike was on hot soft asphalt....not hard packed gravel.

BTW..we really like our cross bikes for the rails to trail stuff. I just had rotator cuff surgury last week, so my riding is over for a little while.