Or perhaps more suitable title should be what is wrong and what is right, to do in a such situation..
If you stumbled upon an animal in agony, and you had no means/knowledge how to help it, would it be an option to kill it, in order to shorten its suffering?
I saw a bird yesterday night that was looking like dying in pain. I had no idea what was wrong with it, and how I could help it, and I was wondering if I should kill it or leave it be... Do I have the right to make such decision? Should I? It's not like we can ask it what it wants...