Midrash su Levitico 14:18

12) (Vayikra 14:18) "And what is left over of the oil which is on the palm of the Cohein, he shall place on the head of the one who is to be cleansed. And the Cohein shall atone for him before the L–rd.": If he placed it (on his head), it atones. If he did not place it, it does not atone. These are the words of R. Akiva. R. Yochanan b. Nuri says: It (the blood) is the left-over of a mitzvah. Whether or not he placed it, it atones — but it is considered as if he had not atoned (in the choicest manner).

"from his foot": From here they ruled: (If she removed the shoe) from the knee-joint down (in the case of one whose foot was amputated), the chalitzah is valid. "his foot": It is written here "his foot," and elsewhere (Vayikra 14:18). Just as there the right (foot is specifically indicated), here, too, the right (foot is intended).