Destroy All Mines

From Glitches

From the game Zanac for the NES.

There's one level (an early level) where you fly through a ton of the round ball enemies, that don't shoot or move around but take many hits to destroy, over water. Use one Number 6 weapon shot on them (the one that blows up everything on-screen) and no more will appear during this entire area. This could happen because because the Number 6 weapon actually kills all enemies that the game has loaded into memory (not just those on the immediate screen), and maybe once you begin that area, the game has already loaded the entire enemy pattern, and thus it's completely wiped out.

Taken with permission from Flying Omelette.