One of the more curious areas of superstition is the "Law of Contagion" – the feeling people have that when an object has been in contact with someone else that it somehow acquires their "essence".
An experiment done by Psychologist Paul Rozin at the University of Pennsylvania tested how strong this was, with distinctly surprising results. They asked people to rate how they would feel about wearing a nice, freshly laundered blue jumper which had been worn previously by someone else – and then varied the fictitious identities of the previous wearers. People felt so strongly about not wearing a freshly washed jumper previously worn by a serial killer that they would have rather worn an unwashed one which had been dropped in dog mess (!)
From the Quirkology of RichardWiseman