If all animals were originally created to eat plants, why do carnivores have teeth designed to eat meat?

We know that the book of Genesis describes the original creation as being "very good." And since death did not exist at the time these various animals were created, how is it then, that so many animals seem fully designed to be meat-eaters? Some produce deadly poisons, others have armored plates as elaborate defense mechanisms. If animals were created to live in harmony, what was the purpose?

Unfortunately, God doesn't give us all the details. All we can do is begin with what we do know and make reasonable inferences. I can think of several possibilities, which are Biblically acceptable, but it may be that a combination of these or some other best reflects the truth.

Option one is that God, in His foreknowledge, knew that soon things would change, and so He created animals with features they would need in the new economy. Or it may be that these features had some other more benign function originally.

Option two is that a great deal more potential for variation was placed in the original genome. At first the animals were designed to live as herbivores, but adopted new habits in the harsher world following the curse. Today, following many generations of variation, adaptation, and selection, animal groups have speciated so much that extensive variation is impossible.

Option three is probably the most biblically based as Genesis 3 speaks of the great changes which resulted from the curse. Plants would grow "thorns and thistles." The serpent would slither on his "belly," cursed along with the rest of the animals. Eve's body style would be changed, making childbirth a laborious experience. Each of these changes requires a DNA alteration, and now instead of being "very good," "the whole creation groaneth and travaileth in pain" (Romans 8:22) due to the presence of sin and its penalty, death.

I suspect that in His infinite wisdom, God completely changed creation, with all things dying and some animals quite vicious, from then on giving eloquent testimony to the awful consequences of sin. From then on, whenever Adam saw one of the animals kill another, he would have experienced remorse for what he had brought on creation.