This illustration is a reminder of the real injury these signs are clues to: internal head trauma. The inside of the skull has lots of sharp edges to lacerate a brain. High velocity trauma can cause bruising of the brain on the side of the trauma, and also the opposite, called ‘contre-coup’ as the brain is bounced around.

When tissue is damaged it tends to swell. As there isn’t much room for expansion within the skull, pressure in the skull increases rapidly with swelling. This can quickly impede arterial blood flow to the brain, leading to hypoxic injury, strokes, and death.