I finished The Serpent and the Rainbow a few days ago, but I haven't had a chance to write about it because of all the other things that have been going on. I know you've all been waiting on pins and needles to find out what happens, so here's how it all ends.
The scientist gets in deep with the vodoun culture of Haiti and finds out that the main ingredient in the zombi poison is puffer fish, similar to the fugu that people eat in Japan. In Japan, fugu is enjoyed as a delicacy, not because it tastes good, but because the residual poison left in the flesh makes your mouth tingle. There is also typically an accompanying adrenaline rush from knowing that you are eating something that could very well be lethal. On average, fugu poisoning results in 3 deaths per year in Japan.
The poison in puffer fish is called tetrodotoxin. It acts by paralyzing your entire body and kills you through asphyxiation when your diaphragm is no longer able to pull air into your lungs. The strange thing is that although you are not able to move or speak at all, you are completely aware of everything that is going on around you. This is important in the zombi poison because the person is able to witness their own funeral and burial, further emphasizing that they are, in the eyes of the culture, actually dead.
The scientist soon discovers the social elements that lead to a person becoming a zombi. Because the victims have been preconditioned by their culture to know how a zombi is made and who would be turned into a zombi, when they are poisoned and then brought out of the grave by the vodoun priest, they are in fact zombified. It also helps that the priest keeps the zombis on a steady diet of datura, a hallucinogenic plant that prevents the zombis from returning to their normal human state.
The way the secret vodoun society works is basically a justice system. If a person breaks one of the seven social laws such as preventing someone from working their land, benefiting at the expense of another or hurting a family member, then that person is at risk of becoming a zombi. It is part of the culture, and any person taking the risk of breaking one of the social laws is well aware of what the consequences are.
The scientist spends the rest of the book trying to find a way to witness a zombi resurrection, but is unsuccessful. We never find out if the drug can be used as an anesthetic during surgery, but I'm sure that someone would have figured it out by now if it was a viable alternative to what we already use. Moral of the story: Be careful not to break any social laws that could get you zombified if you visit Haiti, and eat fugu at your own risk.