Flagellation

Physically, what is happening during a beating is that energy is being transmitted from the top to the bottom's body surface. The cells are compressed, causing nerve cells sensitive to pressure to respond, and in most cases at least some of the cells are unable to absorb the energy and are damaged or destroyed, provoking a pain response too.

Even fairly light beatings cause some tissue damage, though fortunately you can go a long way before damage to the surface becomes life-threatening: a greater danger is in damaging vital organs near the surface, which is why certain areas of the body should be avoided as explained in the notes on Safety.

The impact depends to a large extent on the amount of energy being transmitted, which in turn depends on factors like the force of the blow, the distance the implement travels and its velocity when it hits. The other important factor is the manner in which the energy is transmitted, which will vary according to the implement and the technique used.

Some materials and designs are more efficient at this than others and will consequently require less effort for the same effect. A flexible implement will bounce, with a certain amount of energy reflected back, whereas a heavier, more rigid implement will not, and may cause deep bruising. However, a more flexible instrument will also be easier to accelerate: some of the most dangerous flagellation toys are whips, because the tip can move so fast.

Something with a large contact area, like a paddle, will spread the energy, giving a more superficial effect across a wider area; something with a smaller contact area, like the tress of a flogger, will be more localized but more destructive, and particularly if it has sharp edges, is more likely to cut into the skin. Tony de Blase (cited in Jacques 1993:229-230 and paraphrased slightly here) has summarized the physical factors involved in the effects of different toys as follows:

Flexibility, from inflexible clubs and paddles to somewhat flexible rubber hoses, riding crops etc. to very flexible cats and bullwhips.

Weight: consider a baseball bat versus a chopstick, a fly-swatter versus a paddle, a shot-loaded bullwhip versus a cheap paper-filled Mexican bullwhip and a deerskin cat versus a latigo leather cat.

Contact surface: generally, for equal force, the thinner the implement, the more damage done. Surface characteristics -- a studded versus smooth paddle, flat versus rounded whip tails, knotted versus unknotted whip tails, smooth deerskin versus rough hemp rope etc. -- will also change the feel and force of the toy.

The 'stroke' of the implement with its two distinct aspects, the sting and the thud. A light cat will give lots of sting but little thud, whereas a heavy rubber hose will give little sting and lots of thud. This can also vary with manner of use: a heavy whip laid across the back will give some sting and lots of thud, but, worked so only the cracker at its tip will hit the same back, will give virtually no thud but will cut the skin bloody.