Halloween has always been a holiday filled with mystery, magic and superstition. It began as a Celtic end-of-summer festival during which people felt especially close to deceased relatives and friends. For these friendly spirits, they set places at the dinner table, left treats on doorsteps and along the side of the road and lit candles to help loved ones find their way back to the spirit world. Today’s Halloween ghosts are often depicted as more fearsome and malevolent, and our customs and superstitions are scarier too. We avoid crossing paths with black cats, afraid that they might bring us bad luck. This idea has its roots in the Middle Ages, when many people believed that witches avoided detection by turning themselves into black cats. We try not to walk under ladders for the same reason. This superstition may have come from the ancient Egyptians, who believed that triangles were sacred (it also may have something to do with the fact that walking under a leaning ladder tends to be fairly unsafe). And around Halloween, especially, we try to avoid breaking mirrors, stepping on cracks in the road or spilling salt.