I also refer to God having to kill animals and shed blood in order to make coverings for Adam and Eve...but, of course, this is hind sight. It could be that after the fall man became enemies with the animals they lived with in peace before. After the fall animals attached man...and man killed animals; both for protection and for food.
At the fall the serpent spoke to Eve. And she didn't say, "Now you are talking? What's going on here?" It was the norm.
After the Flood Noah was making sacrifices, if I remember correctly. Anyone else prior? Not that I recall.
The passage in question is far removed even from the Flood. How many generations before Abram?