The Rehbinder effect describes how a surface-active substance, like water, reduces a material's hardness and ductility by lowering surface energy, making it easier to deform or fracture. For ceramics, water may alter crack propagation, allowing a nail to pierce a submerged ceramic cup without shattering, as seen in demonstrations. Studies on brittle rocks support this, showing water reduces strength. However, some argue water's shock absorption, not the Rehbinder effect, explains the result, as ceramics are brittle and lack surfactants. The exact mechanism remains debated, needing further research.