here is an example of what I mean by that let's just say that you were teaching a new Dom the very basics of knife play and you had a sub who is still some what new to the lifestyle helping you out they may hesitate about letting you demonstrate on them so it would be a wasted session due to you not being able to show the Dom what you wanted to show them.

AHA! Now there is the rub, from my point of view. Just a thought here.......

But, in your attempt to "teach" the new Dom, wouldn't a novice sub be more ideal? That way, as she were performing, and a glitch arose, you would then be able to better teach the Dom on how to handle the practical problems that always seem to arise...ie: training/ conditioning the sub to respond in the manner YOU prescribe.

After all, having any D/s relationship, takes much work on both parts, to self train/condition and train/assist the other into their respective role.