h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

My father and several of his friends once used rice to play a practical joke on some poor woman they all knew. It seems she had an irrational fear of mice. They took rice which had been died black (or maybe it was simply rice of a brown variety) and placed a small handful in their pockets before they visited. When their hostess wasn't looking, they would spread a few grains in a drawer or behind the toaster or something. She would, of course, find them and assume they were mouse droppings. This was actually more cruel to here husband than to her, as he had to pay for all the traps and poisons and exterminators, as well as put up with a hysterical wife. This ended up being drug out over several years. The targets never could figure out why they couldn't manage to kill off all the mice. I don't think the jokers ever did come clean...