I used to have a basket on the front of my bike that I used to things around campus, with a bungee net to stretch over the top to hold stuff in. One morning the basket was empty while I was riding between two classes, and I rode off a curb. The bounce from the curve caused one edge of the net to unhook and fall down into the front wheel, where it got sucked into the brakes and completely locked up. Fortunately, I was going slow enough that I didn't fly over the handlebars, but my shin had a very sudden and painful encounter with my spiky mountain bike pedals, and I had to abandon the bike locked to a lamppost and come back to untangle it later so that I wouldn't miss class!