This is weirdly disturbing and disturbingly weird. SeattlePI reports:
New research in biomechanics suggests that young people are developing hornlike spikes at the back of their skulls – bone spurs caused by the forward tilt of the head, which shifts weight from the spine to the muscles at the back of the head, causing bone growth in the connecting tendons and ligaments. The weight transfer that causes the buildup can be compared to the way the skin thickens into a callus as a response to pressure or abrasion.
The result is a hook or hornlike feature jutting out from the skull, just above the neck.
X-rays at the link.