After many Xbox 360 owners reported scratched discs as a result of tilting their consoles between the horizontal and vertical positions, the guys at Llama.com decided to run an investigation.

They painted the whole black laser assembly housing with a silver grey pen, reassembled the drive and did the tilt-the-console-while-it-is-working trick using a copy of Quake 4. After hearing that spooky scratching sound, they once again disassembled the drive to find out what causes the scratches. The following picture shows exactly the areas that produce the scratches.

So there you have it. Switch your Xbox 360 between vertical and horizontal position while playing a disc and rest assured that disc won't work again. As Llama points out, Microsoft does indeed warn about this in the Volume 1: Setup of the manual that comes with the Xbox 360: "Remove discs before moving the console or tilting it between the horizontal and vertical positions."