Stay in the light! This is Moffat's ultimate play on our fear of the dark. Like Listen, he takes a childhood fear and turns into a very deadly threat. This time, it's the shadows, creeping towards us, intent on devouring killing us by stripping the flesh from our bones. In an episode that features the brilliant introduction of River Song, its the image of skeletons in space suits walking towards our heroes with human voices that delivers the ultimate chills, making it a classic with many Whovians. The creepiest moment comes when the Doctor, Donna, River and her companions start to count the shadows cast at their feet. Everyone has one shadow but Dave has two. It's the moment that sends a shiver down the audience's back as they realise the Vashta Nerada have attached themselves to him. At this point we'd already seen the shadows strip the flesh from a chicken bone and now we knew he was doomed. The moment the skeleton inside Dave's suit asks "who turned out the lights?" all our childhood fears of the dark come flooding back...