Prions cause many forms of encephalitis, or brain disease, such as scrapie, Creutzfeldt-Jakob Disease (Bovine Spongiform Encephalopathy) and kuru. Prions work by changing the shape of proteins in the infected animals. While normal proteins have lots of alpha helices, or twisted parts, changed proteins have lots of beta sheets, or flat parts. The word is pronounced "pree-on".