If you're at Valve HQ and turn a corner to find this sentry gun staring you in the face, turn around, quickly.
Design and effects studio Weta Workshop, known for its work on properties such as the Lord of the Rings movies, might be trying to kill everyone at Valve headquarters. Valve recently posted a video on YouTube of Weta mounting a Team Fortress 2 sentry gun at its headquarters.
Weta must have an Engineer working for it, but he's nowhere to be found in the video. The sentry gun is only level one, so it still needs to be upgraded to reach its full Gatling potential, but every aspect from its tripod base to the large red ammo box is spot on.
It works just like the virtual version of the sentry gun found in Team Fortress 2, with a motion sensor included that detects movement for aiming purposes. Valve decided to put it in the company lobby to annihilate any unwanted Scouts, Soldiers, Heavies, Demomen, Pyros, or people selling magazines.
The sentry gun isn't seen actually firing bullets, and instead has lights that imitate a muzzle flash. Valve and Weta claim that doesn't have the ability to kill anyone, but I know that I won't be going into Valve's lobby anytime soon without a cloak or disguise.