The admired sona are monolinear: one line, never lifted, closes around every dot of the grid. Marcia Ascher's Ethnomathematics, which devotes a chapter to sand tracings, states the property in the language of graph theory: such a drawing is an Eulerian circuit, a closed path traversing every edge of its figure exactly once, the structure Euler isolated in the Konigsberg bridge problem, executed here freehand in sand at storytelling speed. The drawers' methods were systematic. The commonest family of sona behaves exactly like a billiard ball crossing a dot grid diagonally, rebounding at the borders; whether the result is one line or several depends on the grid's proportions, and drawers knew, in practice, which rectangles yield the single line that the art demands.
Paulus Gerdes reconstructed further construction rules, showing how master drawers chained small figures into large ones by systematic joins, and how classic designs such as the chased-chicken path arise from simple generating procedures applied with perfect consistency. Gerdes, working in Mozambique, also carried sona into the classroom, arguing that African mathematics education could stand on African foundations, and the drawings now appear in curricula and in the ethnomathematics literature worldwide. The lusona thus closed twice over: a line returning to its beginning in the sand, and a tradition, nearly broken in the colonial century, rejoined to the world's mathematics by patient reconstruction.