Warning: Non-Medieval Content. Unless the oblique reference to Leonardo is medieval.
Reading this article about unoriginal originality brought to mind an old post of mine about the "Kinkade Code," and this earlier post by someone I'd never heard of. After running across that, I googled "Kincade Code" and came up with any number of other posts with the same joke. Some follow my own post, and could theoretically have been influenced by it, but many pre-date it, so short of some sort-of wormhole in space/time, we came up with the idea independently.
As a colleague of mine used to say, "Great minds think in the same rut." Or this, too.