The origins of some of the most obscure English phrases have finally been revealed.
Here we take a look at some of sayings we use all the time, but perhaps don't know why.
'It's brass monkeys outside'
Used to describe cold weather, this saying derives from the traditional Navy phrase "cold enough to freeze the balls off a brass monkey".
This references the brass structure or 'monkey' where cannon balls were stacked.
'Mad as a hatter'
This saying has its roots in the 18th and 19th century, according to experts, when poisonous mercury was used in felting and hat making causing many people to go "mad".
Referring to something being misleading, this phrase has its roots in the training of young hunting dogs.
The dogs were sometimes expected to be able to follow a scent despite the confusing smells of a pinch of smoked and salted herring of a reddish colour being added to the mix.
'Bite the bullet'
Meaning to have to do something unpleasant, this saying relates to how wounded WWI soldiers would bite on a bullet to deal with the pain while being operated on without anaesthetic.
'Skeleton in the cupboard'
This saying means to have something embarrassing to hide and originates from how grave-robbers and murderers would hide remains that they had stolen in order to supply them to medical schools and doctors.
The research was conducted by linguists Franz Andres Morrissey and Jurg Strassler for Privilege Insurance.