Slaps on the face are dangerous. Hitting anywhere in the head is dangerous and, as you probably noticed, the face happens to be at the front of the head.
Never, ever hit with the closed hand, with the fist (that means no, nein, non, não, nyet (or it should be njet?). If you still don’t get it, get a dictionary and translate “no” from English to your language.
But even with the palm and fingers, you could hurt your sub.
First, you will shake the head. That is dangerous because of the whiplash effect on the neck, which could hurt the neck vertebrae, muscles and tendons (or, at the extreme, break the neck). You could hold the punished‘s face with your other hand, for diminishing this effect.
Second, you’ll shake the brains, which will hit against the inside of the skull, producing a small concussion. That is why the slapped gets dizzy and is the reason for the boxer’s knock out. Too strong or repeated impacts could, as in the boxers, damage the brains.
Shaking the head can also detach the eyes retina. If there is any weakness, it could happen with a not too strong slap..... [Finish Reading The Whole Article Here]
[source] Agony & Ecstasy