Magical healing Deers and Foxes?

[Repulsion]

So, I trapped a fox in a pen of signs, and later a deer, and started attacking them with my slingshot. The shots that did hit were quickly negated by a sparkly sound and a green 99 or 100 rising from the Deer or Fox, which I assumed was a healing thing. How are these Deers or Foxes doing it? Can I even kill them? Is there something I need to know about this?

[KoE]

Deer heal things, yes. The fox likely had nearby deer to heal it.

You need to be able to outdamage the healing (which is especially difficult with a whole herd of deer taking turns) to finish them, which requires pretty good equipment/stats. I don't have any hard numbers, though.