Rat’s arse/ass

This is a modern form of Tinker’s cuss and dates probably from WWII, and it's probably American as in 'I don't give a rat's ass', which means 'I don't care'. In idiomatic speech down the years, animals of all kinds come and go according to whim or fashion. One would imagine that the arse or ass of a rat is fairly small, insignificant. and worthless, hence the expression. Some sources give a first citation in print from Leon Uris in 1953 in his WWII book Battle Cry, which gives more credence to a WWII origin from the US Military. And Mark Twain is also accredited as writing 'I don't give a dead rat' in 1884.