Fridge Horror: Tim wears the same shirt every day, reacts very negatively when he accidentally bumps into Phil ("Don't touch me, you freak!"), enjoys making Amanda cry, is obsessed with gaining control over his classmates, and has been carrying a knife around for at least a year. Anyone else get the sneaking suspicion that he's a victim of child abuse, or at least neglect?
Nightmare Fuel: In volume three, the flashbacks to Edwin's past. He apparently was not properly anesthetized before his neutering, and so was fully conscious the whole time. Though it seems to have been an accident on the vet's part, Edwin still has nightmares about it.
The Shadow Clan (Mimi's albino ferrets) are a little unsettling.