Kommentar zu Oholot 1:2

כלים הנוגעים במת וכו' – whether metal vessels or vessels or clothing which require only rinsing in order to be restored to Levitical cleanness and clothing, are defiled like the corpse itself, as it is written (Numbers 19:16): “[And in the open, anyone who touches a person] who was killed or died naturally, [or human bone or a grave, shall be impure seven days].” The person who was killed is like a corpse, and this is the law for all the rest of the vessels. Therefore, vessels that come in contact with the corpse become a progenitor of the primary sources of ritual impurity/אבי אבות הטומאה, but vessels [that come in contact] with vessels ae a primary source of ritual impurity for always second-degree of ritual impurity never become like [those vessels] that are first-degree of ritual impurity.

What [is the case of] three? Vessels touching a corpse and [other] vessels [touching these] vessels are defiled with seven days’ defilement. A vessel that comes into contact with a dead body is unclean for seven days. These vessels are "fathers of impurity." The same is true for vessels that come into contact with these vessels. These too are "fathers of impurity" and are unclean for seven days.

The third: whether a person or vessels, is defiled with a defilement lasting until the evening. But the "third" link in the chain, a person or vessel who comes into contact with a vessel that had contact with another vessel that was in contact with a corpse, has a lower degree of impurity. He or it is impure only until the evening with "first degree impurity."

השלישי בין אדם בין כלים – become first-degree of ritual impurity, and are defiled until nightfall.