The Turkey Vulture is a fairly harmless animal from a practical standpoint (to humans at least), but from a psychological angle, they can be pretty disquieting.
With a wingspan of up to 72 inches (around 1.8 meters) and the scaley looking head and feet (they have no feathers on their head or legs to prevent infection from their diet of carrion), they are sort of fearsome looking. Now imagine you're out walking alone in an old stone quarry, and you gain a following of a half-dozen of them wheeling patiently, drafting on the thermal currents rising up from the hot stone, circling, waiting for you to falter, weaken, maybe break your ankle and not be able to climb back out. There is something in the single minded and patient nature of their attention, knowing that every nerve in their body is waiting for some ill-fortune to befall you, hoping that you will make up their lunch. It's just downright creepy.