en_obs-sn/content/48/04.md

crush Satan’s head

God made this promise in 02:09. This (crushing the head) represents a person stepping on the head of a snake. The head is completely crushed, and the snake is dead and therefore harmless.

bite his heel

This represents a snake on the ground biting a person’s foot. In this case, Satan would cause the Messiah to suffer, but would not destroy him (See: 02:09).