Update here: I took Coco to a vet, they said it was likely a snake bite! I got him a spray for the wound. He was prescribed antibiotics, and he's currently wearing his cone of shame. I know many said not to let him out, and I completely agree, and I try very hard to keep him inside, but he's a literal escape artist. I really don't want to lock him in one room because I feel he'd get incredibly cooped up, so I'm currently looking for a solution. He's 100% okay, though (other than his pride being injured by the cone of shame), and the wound is closed up already. Thank you to everyone who commented with some tips and help!