Skip and skid? If you're oblivious on how to do it: Put your weight forward on the bike (I usually put my chest basically on the handle bars) and use your right leg to push completely back. You have to have the right timing to do so, so wait for your right pedal to be at 9:00 and your left at 3:00. Push as hard as you can on your back pedal, and your wheel should lock up. It takes a few tries, and is easiest to learn the motions on snow, ice, or a wet road.