A side effect of locking the rear wheels, either by shifting into "park," or applying the parking brake, is what we used to call a "dynamite turn." At slightly higher speeds on pavement, or even slower speeds on water/sand/gravel/etc, soon after the rear wheels lock the rear end of the vehicle will begin to come around, and you will be sliding backwards. We used to do it on narrow two lane roads if we needed to make a rapid u-turn. We would slow to 25-30, put the right side tires off of the pavement, slam on the parking/emergency brake, spin the steering wheel to the left, counter-steer as the rear of the vehicle came around, release the parking brake (used to hook the release handle to the window crank- dating myself here I know- with a big rubber band), hit the gas, and shazam, we are now rocketing off in the other direction. Do not try this yourself, unless you are willing to get stuck a few times, and maybe slide into something, until you master the technique...