What is this thing?

This awful creature was, according to my partner, found under or black walnut tree, attached to or emerging from the neck of a very-recently killed bunny that the dog had (killed within the last ~15m). Any idea what it is? More pics available.

It's not smooth like a slug/leech, but has a textured surface. It looks like a grub, but what would a grub be doing attached to a bunny? It has an obvious mouth and anus. She described the mouth part as "hexagonal", which she saw open while it was alive, coming off of or out of the Bunny's neck (it was in or by by a wound it didn't necessarily inflict).

I think it's probably just congealed evil and should be thrown into a fire, along with everything it touched except the puppy, and that's how it's going to get me.

My opinion is obviously tongue-in-cheek, but what is this really?