Cold enough to freeze the balls off a brass monkey.

The origin and true meaning of this phrase is actually totally unrelated to any form of animal or its testicles. Back in time to the period of the Napoleonic War, the great gunships of this time carried many cannons on various gun decks. As an efficient method of storage and delivery of cannon balls to the cannon for firing, a "Monkey" (this term is used to define a table and/ or a rail) made of brass was used to hold the balls. In very cold temperatures the brass would contract or even break thus allowing the cannon balls to roll off the Monkey onto the gun deck. Hence the sailors would say "it is cold enough to freeze the balls off a Brass Monkey".

Picture by Anne Bourne