Half a lesson

This question was apparently deleted (because it was repeated many times). I'm bringing it back:

has asked a question " Half a lesson. ":
The Mishnah of Yom Kippur writes that only eating and drinking are forbidden on Yom Kippur, but not the other tortures. Some of the early scholars write that this is because the other tortures are rabbinical, but the Ya'ara'im write that these tortures are also from the Torah, but they are a positive prohibition. The Ya'ara'im ask – after all, we have seen that a king and a bride are permitted to anoint their hands, and it is fine if the prohibition is rabbinical, but if the prohibition is from the Torah, then why would the sages permit it? And he establishes that the prohibition is on the washing of the entire body, and what is permitted is to wash only parts of it. And in a great light, the difficulty – after all, it was decided according to the method of Rabbi Yochanan, that half a shiur is prohibited from the Torah, and so it would still be a prohibition from the Torah. And the latter establish that the washing of the entire body is a different type of enjoyment from the washing of a part. And I did not understand why the latter did not establish a simple settlement – after all, the issue of the shiur that the Torah gave is the total amount by which one must violate the prohibition and in which one is punished, but in the matter of the case, the amount has no significance and the evidence that if one washes the little finger a hundred times, it simply will not be more than half a shiur, even though quantitatively the washing is equivalent to washing the entire body, and from this we see that washing the entire body is the definition of the prohibition, and to discuss the washing of a portion of half a shiur would be equivalent to discussing eating meat alone as violating half a shiur of meat with milk. And perhaps what the latter hold is this: After all, the law of eating less than a shiur is exempt unless the food was a shari'ah, and then one is also deficient even if it were not so. And we have learned that the issue of the lesson is not quantity but \'\'unit\'\', and that is, it is necessary to perform the forbidden act in a complete unit in order to be punished, and in Alma what defines a unit is the amount of a kazait, except in cases where the thing eaten is a creature. And it is explained in the Ishta that in Nid\'\'d everything that is not deficient when summing up the same quantity but is not a whole body, is because here there are several parts of a unit that did not join into one unit, and what in the case of a sicha the definition of a unit is only a creature, is perhaps because the sicha is in part of a whole body, and the law is that whoever gnaws a piece of the rooster itself will be exempt.. and perhaps it is from the definitions of sicha versus eating. Can the Rabbi explain the difference between sicha and eating, and in general does the Rabbi think this is correct?