It’s a chilly night in northern Wales, and on the set of the upcoming movie Sherlock Holmes, the famed detective is scampering around a candlelit, 400-year-old stone barn, trying to stab a robot. This is supposed to be one of the film’s most gripping moments: a plot-twisting showdown that finds a sword-wielding Holmes battling a homicidal steampunk droid. But because it was choreographed at the very last minute — and because the robot costume is made of plastic and leather — the scene is falling flat. It’s hard to think of anything more anticlimactic than the thup of fake steel hitting fake metal.