They can be a lot of things, like ghosts or ideas people gave power. Or curses.

[another pause, because this is something he's been unsure of.] I don't know. If corruption is like curses maybe, but... I haven't really seen any beasts or anything. [and it scares him, if he's honest, all the corruption stuff. far less so it hurting him and far more it infecting him and how much he could hurt people if that happened.]