The patient is sitting in a stationary car which is run into from behind. The impact is unforseen and the occupant cannot brace his muscles against it. The head is thrown backwards, then equally abruptly forwards, the unprotected joints bearing the brunt. Severe types of damage may be caused - even death - but the common result is a disc-dicplacement, developing in the course of some hours so that by evening, pain prevents the neck being moved at all. Severe stiffness continues for several weeks, then slowly abates, full movement returning after some months; but some degree of discomfort may remain, sometimes permanently. Unless the patient is claiming damages (when there is a tenency for symptoms to be prolonged until the suit is concluded some years later) the pain usually goes in the end, but genuine persistant symptoms, often relievable, are encountered.