Sci-fi and fantasy films are famously fond of twist endings. Certainly, authors such as Richard Matheson and TV shows such as The Twilight Zone are a big reason why - but last-act shocks reach back to the era of silent cinema, as anyone who's seen 1920's The Cabinet of Dr Caligari can attest. Last-act shocks don't always work, but they're almost always memorable. Here are the best and the worst.