Looked into this last time this topic came up somewhere.
Stunning is perfectly in line with Halal.
All that is required of Halal in regard to the actual processing of the meat is that the the animal is alive at the point it is exsanguinated. . . and under usual abattoir practices it is. It does happen however that the stunning process sometimes goes wrong (especially if a bolt gun is the method used) and it itself kills the animal. If this happens then that animal is not considered Halal as it was dead before exsanguination and is therefore considered to be "carrion". Otherwise stunning is fine.
Its also worth mentioning that there are good reasons both in terms of practicality and public health to exsanguinate whilst the heart is still beating and such reasons are probably why these things became part of religious texts in the first place, along with eating shellfish being a generally bad idea healthwise! No idea where the antipathy to pigs came from however, no good reason at all not to eat a pig.
On the other points of Halal slaughter such as the person carrying it out being a Muslim (some say any Abrahamic faith is fine, some say anyone at all is fine) or the meat being killed specifically in the name of Allah (It cannot however be specifically killed in the name of any OTHER god
) there is considerable disagreement within Islam, and thus the definition of Halal becomes somewhat less clear.
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