Impact play is a human sexual practice in which one person is struck (usually repeatedly) by another person for the gratification of either or both parties which may or may not be sexual in nature. It is considered a form of BDSM. There are a number of activities that qualify as impact play. In erotic spanking the sub is struck on the buttocks either with the Dominant's open hand, or a rigid implement such as a paddle, cane or riding crop. In the latter case the activity is often referred to as paddling, caning or cropping. In erotic flagellation the sub is struck with a flexible implement such a whip or belt. Whips are classified by how many falls they have: Single tails such as a bullwhip have a single fall. The associated activity is referred to as single tailing. Floggers, such as a cat o' nine tails have many falls. The associated activity is referred to as flogging. For safety, impact play should be done on areas of the human body well protected by fat or muscle; spots to avoid include the kidneys, neck, tailbone, hipbones, the head and all joints. The usual targets for flagellation are the buttocks and the two areas of the upper back below the shoulder blades. With care, the thighs, the backs of the calves and the chest can be targets as well. Breasts are another potential (but high-risk) target, and should only be used with experience. The use of a whip means that the Dom must take great care to hit the intended target area, and avoid wrapping; when a whip or flogger makes contact with the target area somewhere up its length and the remaining length wraps around the sub's body to deliver a sharp, non-erotic, and possibly injurious off-target blow, such as to the hipbones or ribs. The longer the falls, the more skill is required by the Dom to land a safe blow. Advanced flogging techniques use a pair of floggers employed in a martial arts style alternating pattern, a technique commonly referred to as "florentining" or "florentine flogging." Less common forms of impact play include punching and face slapping. The sensations produced by impact play depend on the area in which the impact is concentrated. Wide implements such as an open hand, paddle or flogger produce a dull "thuddy" sensation. Narrow implements such as a cane, riding crop, belt