Even in the absence of an impact, significant acceleration or deceleration of the head can cause TBI; however in most cases, a combination of impact and acceleration is probably to blame. Forces involving the head striking or being struck by something, termed "contact" or "impact loading", are the cause of most focal injuries, and movement of the brain within the skull, termed "noncontact" or "inertial loading", usually causes diffuse injuries. The violent shaking of an infant that causes shaken baby syndrome commonly manifests as diffuse injury. In impact loading, the force sends shock waves through the skull and brain, resulting in tissue damage. Shock waves caused by penetrating injuries can also destroy tissue along the path of a projectile, compounding the damage caused by the missile itself.