Comic Merch
I suspect there's a really good reason for that.It's story-magic, not science; and I don't think Minna has actually tried to work out anything remotely resembling a coherent quasi-scientific basis for it. I think she writes what she wants to put in the story, and then sometimes works out a partial explanation to fit, but mostly just handwaves it.
My headcanon (with nothing to support it) is that when a group of infected people develop the Rash simultaneously and are kept (for some reason) at close distance of each other, there's a higher chance of a magical "resonance" or "tuning". This connection between infected persons, or animals, reduces mortality and makes their mutations "align", creating those groups that we saw.
I suppose this is the only video-record of beastification… or something...
In honour of our favourite aquatic bovines making a re-appearance, here are some perfectly normal cows...
Nope!
Cyriak's YouTube channel is full of those funky animations There's one (or two?) with hands, too