The Gemara says that an Acilah Gasa (stuffing oneself until he's beyond full) is not considered as eating and if done on Yom Kippur he's exempt from Kareis.
Tosfos asks: the Gemara in Nazir seems to say the opposite. If someone did an Achila Gasa to the Korbon Pesach, granted he didn't do the Mitzvah in the best way, but he did do the Mizvah of eating the Pesach, So Achila Gasa is classified as eating.
Tosfos answers: there are two definitions of Achila Gasa. Here the definition is stuffing oneself until he's beyond full. That is not considered eating since he has no pleasure at that point. However, in Nazir they're defining Achila Gasa to mean a glutenous eating. Though it might be a little distasteful, it's still considered eating.
Rabbi Chaim Smulowitz
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