A drive in the English countryside might take you through quaint towns, past palatial country estates, and even to mysterious Stonehenge. But in recent years, British fields have featured something even stranger: Mad Cow. Not mad as in angry, but mad as in bovine spongiform encephalopathy, or Mad Cow Disease.

This strange disease was first noticed in the UK when British cows were infected by feed containing tainted sheep material. How could you spot a mad cow? The symptoms were often gruesome: agitation, nervousness, loss of muscular coordination, weight loss and impaired locomotive function. Amongst a herd, a diseased cow could be seen stumbling around by itself with odd, jerking movements.

Mad Cow disease attacks brain tissue, causing it to become pitted, like a sponge. Hence the technical term spongiform. What causes the disease is an infectious agent called a prion, which is an abnormal form of a typically harmless protein found in the brain cells of mammals and birds. Prions either enter a cow's brain through infection or appear there via mutation, and then multiply by causing other proteins to become prions. They damage tissue by destroying nerve cells, which leaves holes in the brain.

Although people cannot contract Mad Cow specifically, at least some scientists claim that eating infected beef can cause a related disease in humans called Creutzfeldt-Jakob. Like Mad Cow, Creutzfeldt-Jakob is prion-related, and does nasty things to the brain. So next time you're in England, you might want to think twice about ordering a meat pie. Try the fish and chips instead.