1. The effect of twisting an object in opposite directions from either end. Torsion tests, using rod-shaped samples, allow stable ductile deformation to be studied up to large strain states.

2. In Gastropoda, the twisting of the body through 180° so that the digestive and nervous systems have a U-shape and the mantle cavity, anus, gills, and two nephridiopores (excretory openings) occupy an anterior position behind the head.