<P> Weeping Angels prefer to take their energy from live victims, but if required, they can drain other forms such as that from electric lights (as seen in "Blink") or other electronics . In "Blink," the Angels attempted to steal the Doctor's TARDIS after trapping him in the past . The engine of the vehicle contained enough time energy to feed them forever, but The Doctor stated that the possible damage they could cause "could switch off the sun". Without power, an Angel will start to decay and revert to a stone state even when not being watched . While still initially capable of movement, its speed will also be extremely hindered when close to a starvation point (as seen in "The Time of Angels"), with its range lessened from meters to a partial step . The effects of starvation can be undone by providing the Angel with energy, but it is implied that Angels can no longer acquire energy themselves in this state . A starving Angel becomes less and less active, and if dormant for too long will erode as a stone statue does, or even lose its physical existence altogether (although it can still exist in an image - based or conceptual state). </P> <P> Weeping Angels have also exhibited a startling ability to project themselves through images, suggesting that they are as much conceptual entities as physical ones . A warning in an ancient book on the Angels, found by River Song, states that "that which holds the image of an angel becomes itself an angel". Using this ability, the Angels appear to be able to hijack both audio - visual equipment and organic memory . In "The Time of Angels", an Angel trapped in the vault of the starship Byzantium took advantage of a video screen which was playing footage of it elsewhere in the vessel: the creature escaped by overriding the screen controls and nearby electronic equipment, took over the screen, and passed through it to physically manifest in another location . Weeping Angels can also imprint a mental image of themselves into a person's mind by looking straight into their eyes: the image then gestates and takes over the person's body to manifest as a new Angel . Amy Pond was infected in such a manner where an involuntary verbal count - down indicated her remaining open - eyed moments as a human . She was able to suspend the Angel's gestation (but not eliminate it) by closing her eyes, refusing to let it breach the' filter' of her optic nerve . In the novel Touched by an Angel, a starving angel is reduced to the point where it no longer has a physical being, and instead exists in the image viewed by cameras . As such, whatever is within the sight of the camera is within the range of the angel which retains fast movement, but at the cost of range . Normally, as in "The Time of Angels", the Angel image would walk right out of the screen; but when it is starving, it cannot do so . To stop movement, simply viewing the screen is enough to lock the angel . </P> <P> The Weeping Angels are well known to Doctor Who companion River Song, who appeared in two of the three major stories to date . Professor River Song has mentioned that she studied the Weeping Angels and wanted to learn more about them . </P> <P> In the seventh series episode "The Angels Take Manhattan", despite being removed from New York's history, a lone angel gained a small victory in permanently trapping the Doctor's companions, Amy Pond and her husband Rory Williams, in the past . </P>

Where did the idea of weeping angels come from