After sacrificing the ram of burnt offering, Moses took some blood from the ram of ordination, and “put it on the ridge of Aaron‘s right ear, and on the thumb of his right hand, and on the big toe of his right foot.” He then repeated that same ritual for each of Aaron’s sons. Finally, the remains of the animal were boiled and consumed by the newly-ordained ‘kohanim.’
https://www.myjewishlearning.com/article/ears-thumbs-and-toes/