Actually, in my experience, having to hold any position for an extended period of time is *very* painful. If the slave is told not to move an inch, the sheer act of holding a position is a mental and bodily strain, not easy to uphold.

From personal experience, I have used a former g/f as a reading lamp. A miner's lamp was secured around her forehead, a metal contraption to keep her in a slightly forward leaning position. It did not take long before she started to perspire profusely, followed by jerking and twitching all over her body. And obviously, panting, grunting, snivelling soon sat in. Actually, since we both did not have too much experience with this type of torture at the time, we broke off the punishment after only 45 minutes. Taking her into my arms and consoling a now openly weeping woman, was the biggest treat.

My point is, go slowly, experiment, and never forget that the person you are doing this to is a human being.

SMartie