Tropes. It's like TWD TV show, where they kill people, saw off legs, etc, for getting bitten, and never actually confirm that bites are lethal first...
@Shamz, it's a Chinese cultural thing. Bleeding from the mouth indicates that they're very upset. It's just a visual signal of their mood, you can take it like it's a facial expression.
I feel like I understand more of the references thanks to the excellent translation and notes. I really like the pronunciation guide this time. Thank you.
Bit irritating that he also gets a super OP animal companion. It would be enough if he was just a strong wolf, but to be a legendary beast... what's the point of always giving the MC too much power right away. At least make him sweat for it a little...