The animal cooperation uses the goo to transform the patients into the monsters because It's basically confirmed the stalker was the girl rat. And the rat gives away secrets of the animal cooperation so the girl must've done it first. Also from what I picked up from the news girl she said that they're "changing...going through something" and they is probably the patients turning into monsters. Also The monsters come out of the animal cooperation truck/car/van. To further back up that the animal cooperation is turning patients into monsters: they've been seen sampling the green goo in the thumbnail. Not to mention that the doctor has been turned into a monster and he's locked up in a room in the hospital inside the lobby. I have 2 theories: He's not locked up and he wants to turn everyone else into monsters, or he isn't the boss and they want to keep all their secrets turning anyone who knew them and wanted the word to get out. Anyways thanks for reading my stupid nerdy theory
Animal hospital, me for the art (if it's even art)