How the theme Unintended Effect got implemented:
The enemy ship's physics get influenced by the players bullets. It's often difficult to judge how they'll behave when being hit. Sometimes this results in movements that make your job of destroying all enemy ships much more difficult. Ships can also ram into other ships which makes things very unpredictable and very much unintended most of the time. But you can of course also use that to your advantage. If you're very good at shooting that is.