It might be my packet, the post might have come quick. I was only joking about the long knives, it is an oblong box with small holes in. If you knock it sharply you should hear a rustling/scraping noise, and psssibly a low intermittent hiss. All you need is a large glass tank, at least three feet deep. Throw in two or three live mice, and then open the box in the bottom of the tank, wearing elbow length leather gauntlets. Put in another three mice each day, plus a saucer of Bailey's Cream Liqueur, and the job's a good'un.