Sotah 29B

מטבול יום דשרץ!

from one who immersed that day who was never a primary source of impurity, as he was rendered impure only through contact with a creeping animal, and nevertheless he disqualifies teruma upon contact.

מה לטבול יום דשרץ שכן במינו אב הטומאה!

The Talmud continues to challenge the inference: What is unique about the impurity of one who immersed that day who was rendered impure through contact with a creeping animal is that this impurity can apply to either a person or a utensil, as people and utensils are capable of achieving purity through immersion, and within its type there can be a primary source of impurity. A loaf, however, is food, which can never be a primary source of impurity. It can only be rendered impure as a secondary source of impurity.

כלי חרש יוכיח.

The Talmud answers: The halakhot of an earthenware vessel can prove that the fact that there are primary sources of impurity within its type is not a relevant factor. An earthenware vessel can never become a primary source of impurity, and nevertheless, if it is impure it disqualifies teruma upon contact.

מה לכלי חרש ⁠— שכן מטמא מאוירו!

The Talmud challenges: What is unique about an earthenware vessel is that unlike a loaf, it can render items impure or it can itself become impure from its airspace. An earthenware vessel is the only vessel that does not require direct contact with another item in order to contract or transfer impurity, but can effect or contract impurity through its airspace.

טבול יום יוכיח.

The Talmud answers: One who immersed that day can prove that being able to render items impure through airspace is not a relevant factor. Such an item disqualifies teruma, but imparts impurity only through direct contact and not through its airspace.