Unit cells and their intersections with an inscribed grain for the two deformation stages of the BCCP (top row, first and second panels); the faces of the unit cell at the second critical deformation stage (top row, third and fourth panels); topview of the unit cell before the first critical stage (bottom row, left panel) and after the first but before the second critical stage (bottom row, central panel); and the arrangement of the spheres at the first critical deformation stage as seen in the plane defined by the centres of the three spheres (bottom row, right panel).