It's in the water. To be more specific it's in city water. Some kind of enzyme used to purify drinking water. At least that’s what Tucker was told. It doesn't affect everyone and if you live out in the country and drink well water or softened water you’ll probably be alright. But straight tap water will expose you to it. Apparently it started back in the 40’s and 50's when the government started passing laws for safer drinking water. Not long after that, they realized that there was a side effect to water treatment. So in true government style, they covered it up instead of correcting the problem. They had already invested millions in water treatment facilities, raised property taxes to cover the cost, and passed water laws. They sure as hell weren't going to lose their asses on that kind investment. So they did what the government does best and buried the problem, literally, by passing more laws regarding burials and proper procedures for handling and disposing of human remains. The burden of responsibility was passed off to hospitals and mortuary services, who in turn would receive monetary compensation for their silence. They would be responsible for handling the problem and controlling the situation. Otherwise, they would suffer fines, criminal charges, or worse.
As it turns out, it takes a few days for the enzyme to affect the body. Normally, it takes three or four days after a person died. According to Tucker, a body starts to decompose immediately after death. The body releases enzymes and bacteria like Clostridium Perfringens which in turn makes Gangrene gas. The gas then forms bubbles in the muscles and causes the body to swell up and smell like rotting meat. These enzymes then start to react with the enzymes found in tap water and cause the body to reanimate. Keeping a body in refrigeration will slow this process down by a few days maybe even a week or more. Embalming it will slow it down even more than that. Sometimes it takes several months for an embalmed body to reanimate.