I'm going to play a sound, and I want you to tell me what it is.

It's the sound of a galloping horse, right?

Well, what if I ask you this?

How do you know it's not a zebra?

There's a famous phrase in medicine and epidemiology.

When you hear hoofbeats, think horses, not zebras.

It is essentially a medical variation of Occam's razor.

The idea that the simplest explanation is usually the correct one.

In practice, it looks like this. If you come into the doctor

with cold symptoms, it's probably not Ebola. If your kid has a pink, itchy eye, it's probably

not a flesh-eating bacteria. Generally, this principle holds up, which is why it's referenced in the

pilot episode of House MD. I don't think it's a tumor. First year of medical school, if you hear hoofbees, you think horses,

not zebras. Are you in first year medical school?

No.

But a show like House would never have existed if it was always that easy. Sometimes our first instincts

in medicine aren't always true.

Take for example, stomach ulcers.

For upset stomach, peptobismal is America's leading remedy.

Here's why.

Back in the good old days, we pretty much thought we had peptic ulcers figured out.

They were caused by stress and bad diet.

It was such common wisdom at the time.

...