According to Haziot et al. , the movement of dislocations on the basal plane of helium-4 crystals is responsible for the solid’s giant plasticity. The figure sketches two consecutive basal planes (blue and red atoms) within the hexagonal crystal structure of helium-4. Dislocations (marked by a dashed line) are pinned by helium-3 impurities (in cyan), which have a larger zero-point motion than helium-4. Dislocations can easily slide on the basal plane, enabling large plastic deformations of the crystal when shear stress is applied.