Video games commonly have glitches. Bugs in the software that make the game either appear incorrectly or crash the game all together. Common glitches include character's polygon body parts going through walls, wall & floor textures failing to appear, or storylines that can't be completed. On several occasions in Skyrim I have seen dragons flying backwards! Some glitches can be beneficial to the player, such as free money or accelerated advancement in the game (shortcuts), but most are simply annoying. Most games have at least a few serious glitches.