This early 16th century German rosary from the Metropolitan Museum of Art's collection is a fabulous bit of memento mori, with callow, living mortals on one side of each bead and grinning death's heads on the other:
Each bead of the rosary represents the bust of a well-fed burgher or maiden on one side, and a skeleton on the other. The terminals, even more graphically, show the head of a deceased man, with half the image eaten away from decay. Such images served as reminders that life is fleeting and that leading a virtuous life as a faithful Christian is key to salvation.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.