The National Institute of Neurological Disorders and Stroke describes shaken baby syndrome as a type of inflicted traumatic brain injury that happens when a baby is violently shaken. A baby has weak neck muscles and a large, heavy head. Shaking makes the fragile brain bounce back and forth inside the skull and causes bruising, swelling, and bleeding, which can lead to permanent, severe brain damage or death.

The characteristic injuries of shaken baby syndrome are subdural hemorrhages (bleeding in the brain), retinal hemorrhages (bleeding in the retina), damage to the spinal cord and neck, and fractures of the ribs and bones. These injuries may not be immediately noticeable.

Symptoms of shaken baby syndrome include extreme irritability, lethargy, poor feeding, breathing problems, convulsions, vomiting, and pale or bluish skin. Shaken baby injuries usually occur in children younger than 2 years old, but may be seen in children up to the age of 5.

A spokeswoman for an organization that aims to educate people about the danger advises parents who are about to lose control to immediately put some space between themselves and the wailing infant.

"We advocate that parents, if frustrated, put babies in safe place and walk away," says Amy Wicks of the National Center on Shaken Baby Syndrome. "No child has ever died from crying."