Choco - one point I disagree with you on is the suffering of an animal slaughtered according to Muslim or Jewish religious law (Halaal, Kosher).
The requirement is that the animal is concious and the jugular only is severed, with spinal column left in-tact.
You state that the animal is still alive and feeling pain under Halaal slaughter, whilst it is not feeling pain when it is electrocuted/stunned.
I'll have to dig out the references, but studies have shown that it is the other way round - it is more humane to slaughter whilst the animal is concious than to stun. It is less pleasant for those looking, as the animal does twitch and writhe when slaughtered under Halaal, but is still when stunned. But from the animal's perspective, there is less suffering if they are NOT stunned.
It basically comes down to what pain/discomfort the animal suffers.
The requirement of a sharp knife means that there is no pain when the throat is cut - a bit like a paper cut doesn't hurt until a few seconds after you have been cut. The incision itself doesn't hurt, but when the nerves register the air etc then a signal is sent to the brain and you 'feel'/experience the pain.
The studies measured brain activity and hence the pain the animal would experience. If there is no brain activity, there is no 'experience' of pain.
Sometimes when one gets up too fast, you can feel a little 'light headed' this is because of a sudden drop in blood flow to the brain, and soon passes. This is also a cause of fainting.
When the main arteries feeding the head are cut, there is immediate - instantaneous - loss of conciousness. The brain goes blank before the pain of the cut can be registered. This is not opinion, but was measured scientifically my monitoring brain activity.
Conversely, a stunned animal is not totallly unconcious - and there was brain activity consistent with fear (and also release of hormones that are consistent with fear - and these hormones to make it to the meat, but not to levels that should be harmful) - but the point here is what does the animal experience.
Overall, therefore, the Jewish and Muslim way of slaughter is actually for the benefit of the animal to the discomfort/detriment of the on-lookers who do see the animal convulse. These convulsions ensure that the blood is expelled from the body and the meat is healthier as a result - (note that animals slaughtered after stunning, still have all the blood drained as they are hung upside down and have the same veins severed).
It is perhaps hard to concede that a writhing slaughtered animal that is completely unconcious and unaware, is more humane than a completely still animal - but the brain activities show that is the case.
Stunning animals causes them distress in their final moments of life. Slaughtering according to Jewish and Muslim laws do not.
Hmm - anyone fancy a juicy steak?