There are zombie viruses. Viruses that reanimate you after you die, (Usually a violent death such as being shot bitten, or stabbed.) It can stay dormant in your system until you die. Then you are dead for a good 10 minutes. and BAM you pop back up and 1, don't know who you are. 2 don't know where you are. Your social security number is not yours anymore. You have no rights and yada yada. And depending on what foods you eat, eventually your flesh starts showing signs of deterioration and such.

Mental problems pop up eventually ad the brain erodes with the rest of the body.

Sometimes ending up in cannibalism.
And sometimes really freaky murders.
Axe murdering, hammer hole in the head murdering.
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Oh a heads up. In the movies the only thing that kills is a headshot.. That works, but putting a few holes in the heart actually works. A virus that reanimates would need a working circulation to be able to continue reanimation. The circulation begins to fail little by little, hence the growth of rotting flesh and "Living rigor mortis."