Valve keeps plenty of secrets from the world, locked away and tied down with live, stripped wires above a shallow pool of stale water, surrounded by a moat of baby hippopotamuses -- but this secret got out. Turret Lullaby is a six-page Portal 2 comic that explains the birth of the singing turrets. We don't want to give it away, but it involves a baby, a burglar and a lot of bullets.

This article was originally published on Joystiq.

PSA: Uncharted 3's multiplayer available at Subway