The use of chemical and biological weapons on the battlefield is considered by most commentators — and by international law — as more abhorrent than the use of nearly all other weapons, including ones meant either to kill secretly or to kill terribly, as do fire or burial alive. I ask why this is so. I explore this question through the study of imagery patterns in Western literature and campaigns against food contamination and environmental pollution. I find that the norm against chemical and biological weapons builds upon a taboo against poisons, a prohibition widely accepted in military manuals as distinguishing soldierly conduct from criminal conduct, especially those forms of conduct made criminal by the employment of treachery, invisibility, and transformation.