Cain & Abel were heteropaternal superfecundation twins – the seed of the serpent was Cain, the seed of Adam (aw-dawm') was Abel.
Cain – Abel
Can – able
Cannibal
Get it?
Gen 3:15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.