Not to be too mean to medieval artists, since they're much better at art than I am, but why do they always have such weird-ass anatomy? Would it have been that difficult to have someone pose for reference?
You'll need to find an extended explanation on your own but in essence - religion. The focus is on symbolism, and not on realism as it diverts attention and doesn't help you describe scenes from the bible.
I remember seeing some examples of paintings made by the same artists for secular and religious purposes, and the secular ones were realistic. But it's been quite a few years ago and the only thing I remember is that they might have been Italian painters working in the Eastern Roman empire that were recognised due to the messed up alphabet.
Well it wouldn't really if you couldn't see his face and halo because they're in the furnace, or if his hands weren't obviously in prayer due to the angle.
Hmmm he looks like an owl in order to show his emotions for the martyr? I legit didn't even see his face before you mentioned it, my brain must be going medieval.