In this world of dom-sub, there is always a safe word: a word that is understood between dom and sub to indicate that the sub is in pain or absolutely cannot do something. The word can be a word agreed beforehand, or it can be simply a question, such as “is that a hard limit?”.

There comes a point when the dom knows the sub so well that such a word is not necessary and in turn the sub trusts the dom to look after it in any situation. When that point is reached, a safe word is not necessary. It doesn’t mean to say that the sub is comfortable doing a particular thing for its dom, but the sub knows that it will never be in any danger. Sub can however be squeamish about certain things, or reticent, and in these situations i think that there should be another word or phrase to indicate, not that the sub cannot do something, but rather that the sub will do that thing. And in this case the phrase comes from The Mistress:

“you will do that for Mistress”

When Mistress says these words the sub knows that it has no choice but to do it.