They could've made all the demons humanoid like lion man, but most of them so far have been closer to animal in form.
Not trying to rain on your idea overmuch, but the series does sort of draw a line between "monsters" and "demons", and you seem to be confusing the two (though I could be misunderstanding). We've seen very few actual demons up to the point the translation's gotten to. There's Mikage (who most people actually assumed was human at first, though his "true form" appears less so, granted) and a silhouette of what looks like a young woman with horns in chapter 2 and El-Domo in the same chapter (who is in control of a crow's body, but we see his apparent true face in one panel, which makes him look like an elf), and Daedalus the Machine King in chapter 5 who is covered in bricks and such but I would describe as a humanoid build.
"Monsters" are things like the Ruby Dragon, Al-Majika, Gigantoad, etc. They're definitely more "animal"-like, though, so I definitely get where you're coming from the "veterinary" part. Maybe less so the "vegan" part since Garron was all "nah, bro, eat them slimes, they's tasty" in chapter 5 as well.
