This is not simply a statement of some kind of hostility that would exist between snakes and people but does, albeit in cryptic language, speak of a strife that will be between Christ and Satan and a final triumph of the former over the latter.
How much Adam and Eve understood of it all may be up for discussion to be sure, but that there was a measure of comprehension is clear from the language in the following verses. It is pointed out by James P. Boyce in his work entitled "Abstract of Systematic Theology" that Eve, at least, associated Jehovah and His promise with the birth of Cain. Boyce says this, "Now the record taken in it's strictest grammatical interpretation teaches not only that the promised seed had become a ground of hope for the woman, but that she had learned to associate with him who was to be the antagonist of the serpent the name of Jehovah Himself." [P-260]
Boice then gives an elaborate and interesting word study that winds up with his showing that Eve thought Cain was, in fact, that Jehovah man-child as he gives a well researched documentation of the language that shows her statement was a statement that said, "I have obtained a man JEHOVAH." In other words, she thought her child Cain was Jehovah come in human form. He wasn't. But that child did ultimately come and the heel-bruising of the seed of woman and head-crushing of the seed of the serpent did occur. We know it as the work of the Cross on our behalf.
I think interpretive honesty and our knowledge of Christ allows us to admit that Eve was incorrect in her assumption that Cain WAS that seed promised. But nothing in the language of scripture ever states that she was correct in that assumption either. Her belief that the promised seed would be Jehovah in human form doing battle on her behalf against sin and it's sources and consequences was ultimately brought to pass however. As stated before, it is the work of the Christ of the Cross and that is the message of the gospel.
This is another simple view of Christ presented in the Old Testament much as we saw last time that He can be seen in the garments worn by the High Priest, Aaron, and his sons, the priests.
I love to reflect on how the whole of scripture is a tale of Christ and His accomplishing the work of redemption.