1871H Newfoundland 10 cent mule
In 1871 Ralph Heaton and Sons mint in Birmingham was contracted to strike 10c pieces for Canada and in 1872 it was contracted to strike 10c pieces for Newfoundland. During production of one of these denominations, an incorrect die was used resulting in the pairing of an 1871H Canada reverse die with a Newfoundland H obverse die.
In the early 1870s such a mule would likely have been due to a die mix-up - after all, neither reverse die has an identifying country or province name, and the average Briton would not have been familiar with the designs used on coins in other parts of the world.
The mintage of Canadian 1871H 10c pieces was 1,870,000 and the mintage of 1872H Newfoundland 10c pieces was 40,000: just two mules are known. They were probably struck as part of the Newfoundland mintage as Ralph Heaton and Sons struck Canadian 1872H 10c pieces as well, so the relevant reverse dies would have been at hand in 1872.