Casting defect caused by the mold material when casting with sand molds, similar to scab defects. It is based on the crystal transformation of α-quartz into β-quartz at approx. 575 °C which is associated with significant volume changes and causes considerable tensions in the grain composite. In this process, sand is removed, molten material fills the resulting gaps and thin scratches (scabs) or grooves (rat tails) are formed on the casting surface. Rat tails mainly occur at the mold bottom which is covered with molten material; therefore rat tails usually prevail at the bottom side of the casting.