I was huddled under the Invisibility Cloak at the furthest shore from Azkaban. Pulling the omnioculars out of my bag, I saw that the Island was overrun with a handful of... vampires? Inferi? They seemed somewhat sentient, if rabid. But my Hominem Revelio spell told me that they were dead, despite the fact that they were running and eating people like you'd expect in a muggle "zombie" outbreak. Fast, creepy zombies.