Rashi on Genesis 3:15/רש"י על בראשית ג׳:ט״ו

1ואיבה אשית AND I WILL SET ENMITY — Your sole intention was that Adam should die by eating it first and that you should then take Eve for yourself (Genesis Rabbah 20:5), and you came to speak to Eve first only because women are easily influenced and know how to influence their husbands; therefore “I shall put enmity [between thee and the woman]”.

2הוא ישופך HE WILL BRUISE (or, POUND) THEE— Like (Deuteronomy 9:21), “And I beat in pieces” which Onkelos translates by ושפית “I pounded it.”

3ואתה תשופנו עקב AND THOU SHALT BRUISE HIS HEEL — As you will have no height (not stand erect) you will be able to bite him only on the heel, but even at that spot you will kill him. The word תשופנו is of the same import as the verb in (Isaiah 40:24). נשף בהם “It bloweth upon them.” When a serpent comes to bite, it blows with a kind of hissing sound. Although the words ישופך and תשופנו have different meanings, since they constitute “a play upon words” by sounding similar, they are both used here.