The physical mechanism of blunt impact injuries to thoracic and abdominal viscera is often conveniently described simply in terms of "crush"--this is an over-simplification. Any impact to the torso does result in the rapid displacement of the body wall which may lacerate and contuse underlying viscera, but this simple explanation does not account for pathology at sites some distance from the contact point and does not adequately describe the dependence of the severity and location of injury upon the rate of energy transfer. Quite minor displacements of the body wall may produce serious injury if the body wall velocity is high. The motion of the body wall generates waves that propagate within the body and transfer energy to internal sites. The nature and properties of these waves are discussed in simple terms and the role of waves in the production of the characteristic injuries resulting from impact to the torso is presented.