I was playing Doom on DOSBOX 0.72 on the episode Thy Flesh Consumed and a glitch happened. In the first level I shot and killed the Shotgun Guy and lots of freaking colors were flashing everywhere. Purple, red, green, blue, etc. were flashing on the screen. So I exited out and I went on again and it worked just fine. Remember, I am playing on DOSBOX 0.72 so it might be an emulator problem. From my experience it was very strange.