30 BLOCKS IN PAIL - Kaput Mouse Blocks will kill house mice, white footed mice, deer mice, voles, and Norway and Roof rats. This bait contains warfarin, which is a highly effective anticoagulant containing low environmental and secondary toxicity. Warfarin is one of the active ingredients in rodenticides because it is very effective against rodents at low concentrations. Paraffin is added for resistance against moisture and for durability. The surfaces on the blocks are ridged to encourage rodent gnawing and there is a hole in the center to allow for use in a bait station. Grains are made of quality material to make sure the rodents come back for more.