Something strange happened in one of my saves. I was going around with a stack of poisoned apples to kill guards with to get their uniforms for my personal museum.

When I got to Skingrad, I went into the guard barracks and started getting all the food and replacing it with poisoned apples, but the guards would all get food from a place I had overlooked or previsouly looted and just would not eat the apples.

I decided to plant them directly on the guards and waited a bit, and sure enough they started dropping like flies. Here's where the glitch comes in: a few days later I'm back in Skingrad at the east gate, and the guard to my left suddenly drops dead! I check his body, I check around, nothing there to have killed him. I left and came back three days later to find a new guard.

I talk to this new guard, leave conversation and all of a sudden his health starts decreasing and he dies too. On the third guard I was able to see what was happening: the poisoned apples were respawning along with the guards, so they kept dying, but just that one guard. I'll try the same thing in my new game to see if I can get the same thing to happen again.

According to UESPWiki, NPCs that respawn pass on the poison apple effect, which is why the guards keep dying.http://http://www.uesp.net/wiki/Oblivion:Poisoned_Apple

Ha now that's awesome, good way to make money if you have the patience