I can see how people would mistake this snake for an adder, with it's head smashed in, it certainly gives it almost the right head shape. :S
I kind of agree with most people here, both sides of the fence.
On one hand, if any of us were to find a snake in their home, aggressive or not, the overwhelming reaction would probably be "Oh my god! I'm going to miss it, get the camera!", but the average Joe Idiot does not differentiate between a 15cm Antaresia hatchie and a 20+foot Retic, they just see "Snake", and "Snake=bad".
When people are scared of something, they do not act rationally, which is probably most of the reason that most snake vs shovel incidents do not end well. I understand their actions, which is not to say I condone them.
Although I suspect his reasons were not particularly altruistic, in this instance, if the injuries in the first pic were cat-inflicted, I agree with killing the snake. As someone else said, Shovel to the head is a significant improvement on the death by septacaemia which would invariably follow.
I have killed several animals, all taken from my sister's cats, most recently a garden skink. I stomped on it. Not pretty, but it beat the hell out of any close available method, and in the state the cat had it in, the sooner the better.
While I can understand Blue's reaction, the OP was after all just looking for an ID; I think that the animosity that a lot of members displayed was fairly justified.
If I accidentally ran over a cat, I wouldn't take a photo, post it on a forum full of cat lovers and ask "what breed is this?" Especially with no warning, or indication of the animals state. I think part of what is making everyone so mad is that not only did the OP kill it when it wasn't being aggressive in any way, but also that he is in the midst of a snake-oriented forum, and is not in the least bit apologetic for destroying it.
Incidentally, it's not that I think that animal's lives have equal value to human lives, it's just that I find most people I meet to be worthless.
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Sorry, wrote an essay.