פירוש על עוקצים 3:1

צריכים הכשר (that require preparation) – water, as it is written (Leviticus 11:38): “But if water is put on the seed [and any part of a carcass falls upon it, it shall be unclean for you].” (see also Tractate Makhshirin, Chapter 6, Mishnah 4 for the listing of the seven liquids).

Some things need to be rendered susceptible [to uncleanness] but they do not need intention,
[Other things need] intention and to be rendered susceptible.
[Other things] need intention, but do not need to be rendered susceptible,
[And other things] need neither to be rendered susceptible nor intention.
Any food that is meant for people need to be rendered susceptible, but does not need intention.
The first four sections of this mishnah divide foods into four categories depending on two factors. First of all, whether they need to have been in contact with water in order to be susceptible to impurity (the topic of Makhshirin). Second, whether a person needs to be think about using them for human food in order for them to be susceptible. Our mishnah introduces these issues and then subsequent mishnayot explain and illustrate them. Sections 1-4 are the introduction, section five is explained below.
Section five: This illustrates the rule in section one. Foods that are clearly intended for human use, let's say expensive fruits, need to have been in contact with water to be susceptible. But since they are clearly meant for human consumption, they do not need intention. One doesn't need to actively decide that the food will be used by a human for it to be susceptible.

ואין צריכין מחשבה – to consider them as food, and all of our Mishnah is explained further on (see Mishnah 2 of this chapter).