Two new examples of decorative art have turned up at the Gravettian site of Předmostí, dating to the twenty-sixth to twenty-fifth millennium BP: rectilinear grid patterns are executed on one side of flat bones, probably of reindeer. The authors speculate that the two pieces may have come from a single larger decorated object. The grids themselves join a growing repertoire of patterns known from Upper Palaeolithic society, but their role remains enigmatic: counting, calendars or ornament? Art or science?