"I saw what you did to Delta, can you do it to other mutated animals?"
Earlier before Rex departed to the Dark Elf Kingdom for the Divine Chalice, he came back to the castle and instantly came to meet with Calidora. He had already taken a fresh air to cool his mind, and that was all he needed to push on.
Aside from doing the Race Evolution Quest and healing the Countess, he had one more thing.
He wanted to turn Caraptaros into a Werewolf.
But in order for him to do that, he needs to weaken Caraptaros greatly.
One ingredient, that the System suggested, was a specific mutated snake's venom—but that was suggested, before the Second Breath happened. Now that the world changed, with a lot of ninth-rank realm mutated animals roaming around, he tallied there would be other kinds of mutated snake that could weaken Caraptaros' durability.
Finding them, however, would be a problem for Rex as he has no time on his hands.