Although they seem unrealistic, zombies can be created and are realistic because of these different things that can happen in the brain that can cause a person to behave like them. Parasites and viruses can cause these things, however, viruses are the closest to realism because of the way they can spread. Whatever is wrong with a zombie is probably caused by their brain because of the way they behave. However, to understand all this you need to understand how viruses work. Viruses can do many different things to a body, they can destroy, corrupt and take control of the body's cells. They can damage parts of the body or cause the body to self-destruct, viruses are dangerous but can sometimes be cured. Viruses lack the enzymes needed to conduct life, so they use other people's cells, called host cells, to live and carry out their functions, such as reproduction. Viruses inject their genetic instructions into a cell causing the cell to create viral materials, which become new viruses and usually break down the side of the cell destroying it. Viruses can cause parts of the brain to react and activate, causing behavioral changes. For example, a disease called Toxoplasmosis can alter the behavior of rats, while it affects humans differently than rats, is an example of what viruses can do. The virus switches the triggers that cause neuronal reactions into fear and excitement, so that what causes fear actually causes excitement. This causes the rat to be eaten by a cat and a parasite (which injects the virus) inside the rat can reproduce in a cat. A virus doesn't just go to the brain to cause these things, as there is a "shield" around the brain that protects it from everything. This “shield” is called the blood-brain barrier, BBB, whose molecule...... in the center of the sheet......Web.18 May 2014.-your-brain-epstein-barr-virus -and- multiple sclerosis/>.Freudenrich, Craig, Ph.D. "How Viruses Work." How things work. HowStuffWorks.com, October 19, 2000. Web. May 18, 2014. .Verstynen, Tim and Bradley Voytek. “Diagnosing a Zombie: Brain and Body.” YouTube.YouTube. Network. May 18, 2014. .Diagnosing a Zombie: Brain and Behavior, Part 2. Perf. Tim Verstynen and Bradley Voytek. TED-Ed. YouTube. Network. May 18, 2014. Mayo Clinic staff. "Epilepsy." Mayo Clinic. Mayo Foundation, nd Web. 20 May 2014..