When you hear hoofbeats...

Think zebras

The original phrase was also coined in Maryland by an instructor at University of Maryland medical school

Well, I grew up with neighbors that raised reindeer, so anything is possible

Here's an update on the zebras, teaser alert, they're still roaming PG county

Good advice to stay away from these animals.  I pulled blood from one that was five days old. I went back two weeks later for a repeat sample, and couldn't get it with the zebra pinned against a wall by three big men. They had to turn it loose before one or all of us got hurt. 

I heard a story from a vet in Sarasota about one of his colleagues that had to spend a night in a tree after venturing into a pasture with a zebra. They had to dart it to get him out of the pasture. 

This is a ubiquitous expression in medical school.  The way I learned it, and what I believe is the original version of the expression is, "When you hear hoofbeats, think of horses, but don't forget the zebras."

It combines the thoughts behind these two expressions, "Common things occur commonly," and "You have to think of it to diagnose it."

Breaking news: PG County Zoo Releases Lions!