Programming bugs that you've turned into features

Sometimes you encounter bugs that aren't intentional, but you find a good use out of them or keep them. Are there any that you've encountered when you've created a game, and how have you made use out of it?

Personally, my favorites from dabbling with Adobe Flash are:
- Moonwalking (Explanation: typically this is the result when you have a switch-case statement for detecting key presses, but you don't check when two button presses are held down simultaneously; so then if you have two keys held down, one key is prioritized over the other, so you might have the speed in the x-direction incrementing (meaning the player is walking to the right) while you're facing the left direction.).
- Wall clipping (Explanation: This is usually the result in the axis-aligned bounding box (AABB, a form of collision detection) not being programmed properly. I find this one interesting, because if you turn it into a feature, you can create your own hidden shortcuts and routes).