Natural death of an animal in the nature can be quite long and very painful. The point is not to simulate natural kill, the point is to kill the animal without torturing it unnecessary.
Many animals will start to eat others without bothering to kill them; non-carnivorous birds will peck each other (not particularly quickly) to death, dolphins do gang rape for fun while having the ability to understand what it means, they also kill things like porpoises for fun (they can't eat porpoises and they're neither a threat nor competition to dolphins); predators in good conditions do "surplus kill" i.e. kill just for practice/fun without attempting to eat the victim, apes have been observed to eat parts of other apes while they're still alive, etc, etc.
The main difference between animals is that while less intelligent animals will sometimes simply kill things "just because" even if they don't need to and the suffering will be an accidental side effect, the more intelligent animals will sometimes intentionally hurt/torture others. Morality is orthogonal to intelligence. Romanticizing nature as something pure, "taking only what they need" and beyond evil is ridiculous idealism that doesn't reflect reality.
Not always. Weasels and their relatives engage in surplus killing. Cats regularly play with their prey, clawing them and batting them around for fun, many times without even eating the dead prey animal.
Dolphins are known to devour a shark's liver and leave the rest of the animal to sink, dying a slow death.
Humans are animals. There's almost nothing we do that other predators don't. The difference is that we use technology as a force multiplier of overwhelming magnitude. There isn't much difference in kind, however.
Killer whales will do this to other whales as well (well liver and tongue)
The caracas goes on to feed lots of other things however, and the cycle of life continues.
And then there is this: https://www.newscientist.com/article/dn18454-hippy-apes-caug...
It really messed me up. I won't eat red meat mostly as a result of this, but also because my family were also ridiculously poor cooks. (They were so bad that you wouldn't believe it.)
The smell of the animal fat has stuck with me for nearly thirty years, I can even smell it overpowering the fragrance of perfumed soap. Hand sanitizer, pump soap, and vegetable based soap are fine, but if I have to use ordinary animal soaps, the smell reminds me of what I saw.
I watched a cow be electrocuted, "stunned" they called it. The guide told me that it didn't feel anything because it was in a deep state of shock.
Ever been shocked by a cattle electric fence? When I was 9, I was. You can't move immediately afterward because of the shock of the event, and when the second blast hits you it hits really hard. I felt three of those, it was only when the third struck that I could move, and have no doubt that they were agonizing.
Shocking an animal to stun it, so you can slit its throat and let it die painfully while you dismember it, is no happy little picnic for the beast. This is no easy, painless death. I'm sure it would be agonizing and drawn out over several minutes, and by the time the animal recovers from the shock enough to express its suffering, it's already in pieces and can't.
Roll on lab-grown meat.
Side note: not completely relevant, but I have been attacked by a dog, and I was in shock through that as well. The worst injuries really hurt, but the adrenaline from the attack made me able to get away from the dog. The minor skin injuries I couldn't feel, because the pain centers were being overwhelmed by the worse ones. Between this, and the cattle electric fence, I'm sure they suffer.
I saw a video (which I won't link to you, as I'm certain you don't want to see it) of a phenomenal on-site butcher, he was incredibly precise, fast, etc.
Anyway, the video starts with a live cow, which is killed instantly with a small firearm and a well-placed bullet to the brain.
I butcher animals sometimes (I hunt and have a small homestead) and I would not dream to use any method which involved a death even as slow as bleeding out.
“These ribs are good!”
“Yeah, got me a new butcher. Has a sound proof room in the back. Slow bleeds em’”
If civilization crushed and I would be suddenly living in the forest with family, I would kill the animal however I could - to eat. Probably painfully, because I know nothing else and probably am too exhausted to waste energy. I care more about me and kids not dying then about lobster pain.
On the other extreme, we have cheap pulses to kill them quick available, why not.
The same process happen with everything: legal systems, medicine and even child raising.