I encountered an extremely disturbing graphical/physics-fucking glitch in Fallout 3 before...in the Riley's Rangers intro mission where you're going to get them off the hotel by finding the elevator key in the robot, I remembered noticing that robot in one of the side rooms you fight through right before you get to the top floor. So, I went back in to the bloodied battleground, and began to look.
Everywhere I went I could hear a terrifying clunking, clanging, crashing sound like something out of the worst nightmares anyone's mind could ever spawn. I was shitting myself in paranoia. It felt like everytime I looked the other way or around a corner, a Super Mutant would immediately obliterate me. I was seriously horrified.
Certain places I went, it'd get louder and more ominous, sometimes changing to a more layered, glitched-out, harrowing tone like some crazy industrial music. I was checking every room, in fear for my life, for the goddamn robot, too. One room I went in, I noticed something moving ever so slightly...I went to check it out with my light on, and could tell the...thing...was moving in time with the sounds I was hearing. Sure enough, there was my robot, half-fallen through the floor. I procured the goddamned elevator key from it after a lot of work (getting my character to be able to interact with the thing was hard because halfway through floor apparently means that he doesn't even exist), and a lot of brick shitting.
Fuck that was scary.