The Vinculum is the artificial love and loyalty spawned by feeding from the same vampire three times. Part of the Kindred's ill regard for tasting the blood of other vampires is the Vinculum. Those Kindred who consume the blood of another single vampire three times become subjected to a unique state of emotional control. This Vinculum creates a powerful but artificial love for the vampire from whom three draughts are taken.
A thrall is not a complete slave of his master, but he is close. He constantly feels the artificial love, affection and loyalty imposed by the bond, even if he simultaneously hates his domitor for demeaning or enslaving him. Among those who are weak-willed, naive, mentally unstable or even willing, the blood bond creates a feeling of singular devotion.
There can also be a mutual form of protection stemmed from this, as kindred under a third-level blood bond are immune from the Vinculum of others. Furthermore, any lesser blood bonds the thrall was already bound to instantly break. Kindred who deliberately drink of each other's blood for this reason create what is known as a perversion, as they will do anything, even break the Masquerade or risk the light of the sun, in the name of their undying love.
Though difficult, there are other ways to break a Vinculum. Sometimes the simple passage of time can weaken a regnant's hold, while in other cases, only the death of the domitor can break the bond.