In the previous Mishnah, we learned that according to Torah law, a worker engaged in harvesting ripe produce, as well as one working with detached produce whose processing is not yet finished, is permitted to eat from it.
The source of the permission and its resulting implication:
The basis for the permission to eat while working with detached produce is derived by comparison to the verse, "Lo tachsom shor bedisho" - just as it is forbidden to muzzle an ox while it threshes, so too, from a halachic perspective, one must not muzzle a worker engaged in his labor, and he is permitted to eat.
This raises a logical assumption: Since the permission is derived from an ox, perhaps it is required for the worker to work in the same manner that an animal works - with his entire body, using his hands and feet simultaneously; whereas one doing more limited work, with only his hands or only his feet, is not included in the permission. However, this is not the halachah: Anyone engaged with the produce, with whichever limb it may be, if the produce is at the permitting stage - the Torah permits him to eat, as explained in the previous Mishnah.
The language of the Mishnah:
"Hayah oseh beyadav aval lo beraglav" - if he was working with his hands but not his feet, sitting in place and processing the produce only with his hands.
"Beraglav aval lo beyadav" - with his feet but not his hands, such as one threshing with his feet in the manner of an animal, or treading grapes to extract the juice, without using his hands.
"Afilu bechetefo" - even with his shoulder, meaning even if he does not work with his hands and feet at all, but only uses his shoulder, acting as a sort of table upon which things are temporarily placed.
In all of these cases it is stated: "Harei zeh ochel" - he may eat, as the rule is that if the food is at that stage, the Torah permits him to eat from it.
The opinion of Rabbi Yosi beRabbi Yehudah:
The Mishnah brings a dissenting opinion, which is not accepted as halachah: "Rabbi Yosi beRabbi Yehudah omer, ad shaya'aseh beyadav uveraglav" - the worker may only eat when he works in the manner that an animal works, with his hands and feet together. For example, one walking back and forth in a vineyard and picking grapes: he moves his feet and picks with his hands - this person is permitted to eat from the grapes; but one sitting in his place and working with only one limb - he may not eat.
The Halachah: The halachah does not follow Rabbi Yosi beRabbi Yehudah, but rather the first Tanna - anyone engaged in working with the food is permitted to eat from it, provided it is at the appropriate stage, as was explained in the previous Mishnah.