Reference for Yoma 115:8
איכא דאמרי הכי בעי מיניה דרך שירות בכך או אין דרך שירות בכך תא שמע דתנא דבי רבי ישמעאל (במדבר ד, יב) את כל כלי השרת אשר ישרתו בם בקודש שני כלים ושירות אחת
Come and hear: If he stood upon any vessel, or upon his fellow's foot, it is invalid!<span class="x" onmousemove="('comment',' If the priest, in receiving the blood, stood upon a vessel, then that vessel was interposing between the floor of the Sanctuary and the priest, therefore invalidating the service. (Zeb. 24a) . Similarly, if he stood upon his fellow's foot. The foot, however, is homogeneous and the fact that the service is cancelled, would seem to indicate that homogeneous matter is considered an interposition, so that the question above would appear to be answered.');"><sup>4</sup></span> - It is different with his neighbour's foot, because he [his fellow] does not abandon it.<span class="x" onmousemove="('comment',' Homogeneous matter is not considered an interposition, but a human foot is an undeniable entity.');"><sup>5</sup></span>