The library square with the points on is our sharpest, roughest feeling square. It provides a deep tissue stimulation effect when pressed hard but will not damage or hurt your skin. It might encourage you keep your fingers moving over it providing that comfort of moving while sitting still. Some people find it helps them concentrate, others find it distracts them from a situation they are worrying about. Sensory preferences are entirely personal and you may find your preferences change on a mood basis which is why we recommend you buy at least three textures to enjoy.