Just The Tip
Most do not understand and even more don't care that in general, a sadist needs are similar to those of the masochist only in the fact that both are usually sexually charged and to go without a fix, one becomes grumpy. In perspective, a sadist needs to hurt someone. This is one side of the coin to the other side being a masochist needs to be hurt. This is knowingly soothed to feel loved and whole, that everything is okay.
This movie, as are so many others from Sensual Pain Studios, plays out the needs of Sadomasochism. If you were in the room, you could feel the tension just melt away as the scene unfolds. Master James is compelled to hurt his slave by flogging her repeatedly because he needs to love her the way they both understand, as you can see from the tears of painful joy running down face of slave abigail and the laughing from brief light play with the sharp knife.
So, "Just The Tip" is a metaphor used here for the tip of the knife in the knife play, "Just The Tip" of the dong on the stick as the slave is flogged and "Just The Tip" of sanity as it plays out in this multifaceted Master⁄slave dynamic.