The line comes from 'Blink,' the 2007 Doctor Who episode written by Steven Moffat that introduced the Weeping Angels, stone statues that move only when unobserved. The Doctor, trapped in 1969, leaves the warning on a DVD recording for Sally Sparrow. The episode became one of the show's most quoted, and the short warning detached from it online as a standalone horror cue. Its brevity and plain delivery keep it reusable far beyond fan edits, wherever a still object needs to feel quietly lethal.