Commentary for Oktzin 3:1
יֵשׁ צְרִיכִין הֶכְשֵׁר וְאֵינָן צְרִיכִים מַחֲשָׁבָה, מַחֲשָׁבָה וְהֶכְשֵׁר, מַחֲשָׁבָה וְלֹא הֶכְשֵׁר, לֹא הֶכְשֵׁר וְלֹא מַחֲשָׁבָה. כָּל הָאֳכָלִים הַמְיֻחָדִים לָאָדָם צְרִיכִין הֶכְשֵׁר וְאֵינָן צְרִיכִים מַחֲשָׁבָה:
There are those [foods] which [before they can be rendered impure] require being primed [for impurity, by becoming damp] but which do not require intentional thought [designating them for human consumption]; and [there are those which require] intentional thought and being primed; and [there are those which require] intentional thought but not being primed; and [finally, there are those which require] neither being primed, nor intentional thought [before they can be rendered impure]. All foods which are designated for human consumption require being primed, but do not require intentional thought.
Bartenura on Mishnah Oktzin
English Explanation of Mishnah Oktzin
[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.