Further, ideograms - notably, repetitions of spirals - point to both abstract ideas, religious observance, and some astronomical knowledge of lunar and solar cycles. Decorative objects - rock crystal arrowheads, floral- and zig-zagged patterned stones (pedras de raio) and ceramics, deity sculptures - also suggest the development of local systems of craftsmanship, hierarchy, magic and celebration.[13] Recent studies of idol plaques have speculated that they depict some kind of owl deity, with their engravings acting as a means to identify the individual buried by clan, marriage and lineage.[14]