Zevachim 24 - How Do the Kohanim Stand on the Floor
If a Kohen was standing on a utensil, on an animal, or on his colleague’s feet while receiving the blood, the sacrifice becomes invalid.
It was indeed necessary to give all three examples. If we only knew about a utensil, we could have thought that it invalidates the service because it is not flesh. And if we knew only about an animal, we could have said, that is because it is not human flesh. Therefore, the rule in fact taught all three prohibitions.
If the Kohen stood with one foot on a vessel and another one on the Temple floor - we analyze the situation: if the vessel can be removed and the Kohen would still remain standing, the service is valid.
Rabbi Ami asked, if one stone was removed and the Kohen stood in the hole, what is the law? Given that King David sanctified both the upper level of the floor and the lower, the soil can serve as the floor, but is it proper to do the service that way? The question remained unanswered.
Rabbi Shimon permits to receive blood even with the left hand.
Art: John Singer Sargent - Feet Of An Arab, - Tiberias