It's funny how often that happens. A favorite example: https://en.wikipedia.org/wiki/Two_pounds_(British_coin)#Desi...

In case anyone else couldn't tell from the image and didn't want to read all of the history:

> An oddity of the design is that it depicts nineteen interlocking gears. Because there is an odd number of them, the mechanism could not actually turn.

That's not the case for the two pounds though. In the coin's situation, it's because the three gears at the top are interlocked and jammed.