An expression used by antisemites to promote Holocaust denial in covert ways. It refers to the popular denial argument that the gas chambers found in death camps could not have been designed for the purpose of genocide, as some of them were found to have wooden doors which would not be able to hold poisonous gas into the room. Memes featuring this symbol often bear few, if any, other references to the Holocaust, making them incomprehensible to people outside of the in-group.