Some people casually say 'touch wood' when they speak of something they hope will happen. Others won't allow peacock feathers into the house. And almost anyone who finds a four-leafed clover will treasure it and keep it. Why? Some superstitions are so ancient and have been practised for so long that they have come to be regarded as just harmless and widely observed 'customs', without people realising they are basically superstitions. For instance, many people wouldn't bother tossing spilled salt over their left shoulder or avoid walking under a ladder. But they happily continue to wear a wedding ring and blow out candles on a birthday cake.