It is often stated that the phrase originated from the use of a certain metallic tray, called a "____", to hold cannonballs on warships in the 16th to 18th centuries. Supposedly, in very cold temperatures the "___" would contract, causing people to remark, " ___X___"
Later on, a humorist personified this phrase in the form of a patent for the picture below. He says that it works upon the conditions and principles of the phrase __X__, such that when a preset optimum climatic conditions are achieved, it shall cause a noise, emanating from the result of the phrase, as an indication that it is "_____X______"
SO ID X, the phrase in question (or in reply to the question asked)
(Filling in the blank would only give you part of the phrase)
