A beef with beef. Mad cow epidemic.
From Why Files: Science behind the news

Nova Online : The Brain Eater
What causes Mad Cow disease? Is there a new type of infectious agent - a prion - that's responsible? What happens when science faces an unknown pathogen, and what are the implications for public health? Explore these questions and more.

Mad cow disease (emedicine health)

Mad cow disease and humans (About.com)

Frequently asked questions about Mad cow