This trope commonly consists of a scene being well under way when the audience becomes aware of an entity or object being in the scene, and they were unaware of it beforehand.
Usually the object or entity is in the background and moves to the foreground, but there are plenty of other ways for it to happen. Often times the awareness is created by movement, but can also be from lighting or a different camera angle. The awareness is also commonly made through a sudden Jump Scare, although many times it can be a slow reveal.
A more specific and closely related trope is The Calls Are Coming from Inside the House.
- In The Snorkel, the killer is revealed to have been under the floorboards the entire time.
- In The Gallows, there is a scene where the hangman moves forward from the dark background and drags the girl in the scene into the background. Coincidentally, he does this via the Ankle Drag trope. Bonus fact: This scene appears on the poster on the film's IMDb page.
- The shapeshifting creature in Red Dwarf that acts as a vampire on emotional energy is there in the galley on the Dwarf, but is only noticed when Kryten realises there's one kebab too many on Lister's plate. The extra one is of course the emotion-eating monster.
- In the Five Nights at Freddy's franchise, there are several camera angles where the animatronics are in the background and can go unnoticed due to the lack of proper lighting, in line with the theme of the game.
- In a Five Nights at Freddy's 3 video posted by Let's Play, Gavin experiences it firsthand when Springtrap is partly present in the doorway, and loudly yells that Springtrap was there the whole time.