Foucalt once argued that somewhere in the late 19th century corporal punishment had been replaced by a solitary "mental anguish".
Similar arguments then also claim that "breaking on the wheel" represented royal central power, and later powers would be more divisive.
What constitutes "cruel and unusual punishment" to the US power? Paddling, drowning, whipping or "rendition"?
Where does cruelty begin, and torture end?
Please illustrate the reply where possible.

Torture would be without apparent reason, or at least for the sole purpose of inflicting pain without reason. Corporal punishment is not supposed to be about inflicting unnecessary pain for no apparent reason, rather to teach (harshly) through consequence. The difference between the two are as black and white.

Torture is the purposeful act of subjecting an unwilling recipient to pain and anguish which you control and the recipient cannot avoid.

The reason for carrying out the act is not relevant to what torture is.

If you connect the two, you get into the whole nonsense of 'justifying' it.