- a Sheretz Met is an av hatuma
- A kli that touches it can become rishon
- Food that is put in the kli becomes sheni
- Truma that touches the food becomes shlishi
- Kodshim that touch the Truma becomes revii
Rav Wolf points out that there are two ways two understand this passage of Tuma from object to object:
1. Tuma Weakens as it is Passed On
Tuma weakens as it is passed on. The various categories of Av and Vlad hatuma represent the current strength of the Tuma.
2. Avot and Toldot
Only avot pass on tuma. Toldot are tamei but cannot pass it on. Truma/Kodshim become pasul but not tamei. Rav Aharon Lichtenstein suggests this explanation based on the Gemara in Bava Kama(ב.) that compares levels of tuma with Avot and Toldot from Melachot Shabbat(שיעורי הרא"ל טהרות עמ' 85).
Difficulties with Both
In any case, I wanted to bring-up this chakira now since it is so basic and will no doubt be relevant in numerous places in the future.