HUMAN MALE HEADS COMPOSED OF SOLID BONE.
Or at least 2 of them are.
One time, my 3 year old cousin put the family car in gear and rolled the car down the driveway over her 1 year-ish old sister, who was crawling around. She had the big tire mark all the way across her abdomen and nothing broken, nothing 'sploded. True to form, they are tough bitches in adulthood too, having gotten full scholarships to college for volleyball and basketball.
Apparently, getting run over is more easily survived by some folk than others.