Cover a common barrel with stiff paper, tying the edge around the barrel. Place a board so that the rats can have easy access to the top. Sprinkle cheese or other bait on the paper, and allow the rats to eat there unmolested for several days. Then place in the bottom of the barrel a stone 6 or 7 inches high, and pour in water until all the stone is covered, except for a space about big enough for one rat to crawl upon. Now replace the paper, first cutting a cross in the middle. The first rat that climbs on the barrel-top goes through into the water, and climbs on the stone. The paper comes back to its original position, and the second rat follows the first. Then begins a fight for the possession of the dry place on the stone, the noise of which attracts the others, who share the same fate.