A bullet striking a skull leaves distinct entry and exit marks. The skull is made of hard inner and outer surface bones and a soft, spongy layer in between. When a bullet strikes the outer surface bone, its impact leaves a clean break on the outer surface bone due to its hardness, but it leaves beveling on the inner bone side due to the spongy layer in the middle. Therefore, a bullet entry point shows a clean break outside with beveling on the inside. In reverse, the exit wound leaves a clean break on the inside and beveling on the outside of the skull.