It looks like it's somewhat unclear. Here's the first reference I've found, which appears to be reasonably trustworthy at first glance. Note that it's very muc

It looks like it's somewhat unclear. Here's the first reference I've found, which appears to be reasonably trustworthy at first glance. Note that it's very much from the perspective of industrial farming. https://www.grandin.com/humane/meatfocus7-92.html https://www.grandin.com/humane/meatfocus7-92.html Basically, there are studies showing that pigs die a suffocating death with CO2, and there are studies showing that they don't even know it's happening. Both could be true, if there are genetic differences that impact the suffocation response. According to the article, those same differences seem to be present in humans as well, when exposed to high (but non-fatal) concentrations of CO2.