Oktzim, Chapter Three, Mishnah Two
This mishnah lists things that are not human food and therefore are not susceptible to impurity unless someone decides that they are going to eat them (some of these are a bit gross, so beware). They also require contact with water to become susceptible.
1) That which has been severed from a human, beast, wild animal, bird, or from the carrion of an unclean bird, and the fat in villages.
2) And all kinds of wild vegetables, except for truffles and mushrooms;
a) Rabbi Judah says, except for field-leeks, purslane and ornithagolum.
b) And Rabbi Shimon says: except for cynara sycaria.
c) Rabbi Yose says: except for muscari comusum.
3) Behold all these need both intention and to be rendered susceptible [to uncleanness].
Section one: Pieces of flesh cut off of a living human, beast, wild animal or bird are not impure. If one decides to eat them (this is not allowed, but someone might do it) and they come into contact with water, they become susceptible to impurity.
The carrion of an unclean bird is not impure (see Toharot 1:3). Therefore, a piece of flesh cut off from it has the same status as the other meat.
Section two: Wild vegetables generally are not eaten. There are however some exceptions. The first opinion and various other rabbis cite some exceptions. I don’t know what some of these are and the translations are mostly from Albeck. Suffice it to say that these are wild grown vegetables that seem to have been eaten.
Section three: This is the summary of category two from yesterday’s mishnah. In order to be susceptible to impurity these things need to come into contact with liquids and one needs to actively decide that they are going to be eaten.