The 1984 coin with the late Queen Elizabeth is correct on this side but a small detail on the coin's other side is what makes it so unique. The error, also known as the coin's cud, occurs when part of the die breaks and creates a cavity 'which allows for the space to be filled by the planchet (or milled blank) when being pressed into a coin', according to Currency Australia.
You can't buy so much as a lollie from the cornerstore with it, but collectables website Downies says this two-cent coin is worth $495. Downies says the mintage is the second-lowest on record for two-cent coins, meaning there are very few to be had. The 1979 50-cent piece has a rare error - two bars behind the head of the emu. Check your pockets - this 20-cent piece has a tiny alteration that makes it worth thousands of dollars. When Australia switched to decimal currency in 1966, the country sought the aid of Royal Mint in London to create the vast stocks of new coinage needed
Coin Rare Error Cud Collectibles Value 1984 Two-Cent Coin Mintage