9. The Hidden Dancing Boy - Insidious
One of the most memorably creepy moments in the first Insidious occurs when Renai (Rose Byrne) encounters the spirit of a young boy dancing and running around her house, backed by Tiny Tim's sublimely disturbing "Tiptoe Through the Tulips" no less.
But it gets even eerier if you're attentive enough to spot an added secret hidden in plain sight. Before Renai actually comes across the boy, he can be briefly seen standing facing the wall as she puts some clothes in her laundry basket.
Our attention is supposed to be focused on the laundry basket, and to the casual observer the boy just looks like a jacket hanging on the coat rack, but anyone who dared inch their gaze slightly left would realise the shocking truth for themselves.
It's low-key the most horrifying moment in any of the Insidious movies.