Especially when you're swarming commoners with them and the ungodly shrieks are causing more than a few of the poor townsfolk to stop dead in their tracks. The vargouilles wrapping their wings around their horror struck faces as they slide the long sinuous double tongue into their mouth and down their throat, depositing their unholy spawn there to start the cycle anew.
That...and stumbling onto a town where everyone's head is missing is just a great way to screw with players.
edit: grammar