We know that a black cat doesn't determine what our day will look like, yet we knock on a • We don't really think that a ladder overhead will invite disaster, but prefer to bypass it • And if we come across a flip-flop, there are those who will immediately turn it around • In the run-up to Friday the 13th, here's why we continue to act as if there might be something to the superstition - even if we know there isn't