The big fashion in torture is to devise situations in which the victims inflict pain on themselves. These techniques have spread around the world. You can confine the victim in a small box for a few days so that the pain is inflicted through muscle cramps, or you can shut the victim in an outhouse or in a box with a decaying corpse so that the pain is inflicted through nonstop retching. The great virtue of these techniques is that they don't leave marks. If you tie someone's wrists behind their back and then hang them up that way, you'll cause plenty of pain, but you'll also yank the nerves hard enough that the doctors have something to testify to in court.
Electricity burns the tissues.
And so on. But there are gray areas. For example, the doctors are trying to figure out why victims from some of the more advanced countries appear to have deep brain damage that is not consistent with anything so crude as blows to the head.