In BDSM different rituals are used to establish roles and framework of the relationship.
It is similar to how people greet each other in casual integration.
Since nature of this relationship is unequal, each Master and slave have their unique role and place in these rituals.
For example, a collar, that is placed on the neck of the slave, indicates that she is a property of her Master. Similar to how pet (dog) owners place collars on their pets to indicate. Collar reminds slave that she is owned by the Master and bound to his will. When Master sees her with his collar on her neck, he knows she is his.
Only slaves wear collars, because slaves belong to Master and not the other way around. Master do not belong to a slave. That is different from a traditional marriage ceremony of exchanging rings, that instead indicate a sort of mutual bond.
A leash may be attached to the collar to further emphasize this connection. Leash can be freely handled by the Master, indicating his control over the relationship. On the other end leash is firmly attached to slave's collar, indicating that her life and fate is not hers to control and is in Master's hands.
Slaves kneel before Master, to show their respect and submission to him. When there are on their knees, they even look much smaller compared to standing or even sitting Master. That show both of them that Master is big and important, and slave is small and insignificant. Slave kneeling before Master, shows him that she understands and accepts that she is less important than he is.
Ideally slave should kneel all the way to the ground. That is called genuflection, kowtow or dogeza in Japanese. That shows that she is as low as his feet is. Master then can step on her head or back with his foot to further show, that he is above and superior. She is fully inferior and completely below him in every way. Similar to how commoners kowtow before Chinese Emperor or Muslims before their God. This ritual too shows that slave hold her Master in equally high regard.
Slave can also lick Master's foot, to further show him her affection. As affection of an inferior being for superior one. Lowly slave girl cannot dare to go higher than her Master's lowest body parts, feet, so she licks there. She should attempt to clean his superior foot with her lowly tongue.
Similarly, it is slave who should lick/eat their Master's ass, not the other way around. That shows that she will gladly take any shit he will throw at her. His waste is her food. That shows that she accepts her inferiority compared to him. Her face belongs between his butt cheeks.
Similarly, it is always Master who whips, slaps, spanks or beats his slave. That is a way for him to show his both his status and power as well as his strength compared to her. Holding various corporal punishment implements, such as crop, whip or cat-o-nine tails shows that master wields that kind of power.
If a slave touches these implements, for example to bring these implements to her Master, she should never hold them on the handle. Holding them by the handle implies that she wishes to claim his place and power as her own. Therefore, she should avoid doing so, in thus acknowledging that power to punish and inflict pain belongs to Master alone.
Similar to how when a sword is presented to a King by one of his servants, the servant does not hold it by a handle, but rather rests its blade on his open palms. Slave girl too should present crop to the Master in similar fashion, acknowledging that this power is his alone to wield. See picture below for an example.
