How can a seemingly trivial head injury kill you?
To answer this, you need a little anatomy.
Your brain is a pretty important organ, and is well protected. It sits inside a thick armor (the skull) and floats cushioned in a bath of cerebral-spinal fluid. It's surrounded by several layers of tissue, and its blood supply is kept relatively separate from the rest of the body (the "blood-brain barrier"). This separation helps keep out toxins and micro-organisms (but is imperfect). Just beneath the skull is a tough, leathery layer called the dura mater. This picture shows the skull cut…