In the illuminated manuscripts of the 13th and 14th centuries, the margins are often decorated with images of armed knights fighting snails. “This has created a good deal of puzzlement amongst art historians and book historians, wondering just what do they mean?” University of York scholar Kenneth Clarke told the BBC. “The basic idea is the overturning of existing or expected hierarchies,” suggested University of Chicago art historian Marian Bleeke. “It is supposed to be surprising and even funny — I think we get that implicitly today,” she says. Art historian Lilian Randall found 70 examples in 29 books, most...