Yevamot 56A

מכאן ואילך ⁠— אינו אלא נשיקה, ופטור עליה. ופליג אדשמואל.

From this point forward, insertion of anything less than the corona is only considered a kiss, for which he is exempt. And this statement disagrees with that of Shmuel, who maintains that one is liable to receive punishment for external contact of the sexual organs.

אחד המערה ואחד הגומר ⁠— קנה. מאי קנה? רב אמר: קנה לכל, ושמואל אמר: לא קנה אלא לדברים האמורים בפרשה: לירש בנכסי אחיו, ולפוטרה מן הייבום.

§ It was taught in the Mishnah that both one who merely engages in the initial stage of sex and one who completes the act of sex have thereby acquired the yevama. The Talmud asks: What does it mean that he has acquired his yevama? Rav said: He has acquired her for everything. In other words, she is considered his wife in all regards. Therefore, if he is a priest, she may partake of teruma. And Shmuel said he has only acquired her with regard to the matters stated in the chapter of levirate marriage, i.e., to inherit his brother’s property and to exempt her from levirate marriage if he then dies and leaves behind children from another wife.

מן הנשואין ⁠— לדברי הכל אכלה, דהא הות קאכלה מעיקרא. כי פליגי מן האירוסין. רב אמר: אוכלת, דהא רבי רחמנא ביאת שוגג כמזיד.

The Talmud adds: If she was a yevama from marriage, everyone agrees that she may partake of teruma after the initial stage of sex, as she was already partaking at the outset, when she was married to the deceased brother. Therefore, even a minimal act of sex is enough to allow her to continue to partake of teruma. When they disagree it is with regard to a yevama from betrothal. Rav said: She may partake, as God includes unwitting sex and the other forms of sex listed in the Mishnah, and considers them like intentional sex.