You obviously remember that on the May 20 Grey's Anatomy season finale, a madman with a gun and a grudge walked in and went on a shooting spree at Seattle Grace Mercy West.

It made for gripping TV, but one thing some critics have pointed out is the perceived lack of believability - would anyone off the street really be able to roam freely as Gary Clark did?

TV Guide explored this very subject yesterday, and according to Dr. Glenn P. Kelley, cardiologist at East Jefferson General Hospital in Metairie, La., it's both very possible and unlikely.

"Patient room doors do not lock," he says, "so doctors can get to them if we need to."

On the flip side, "supply rooms, pharmacy rooms, and rooms with sensitive/expensive equipment and call rooms all definitely do lock." Oh, and there are entire wards that do as well.

Maternity and psychiatry, for example, are kept on 24/7 lockdown to prevent the wrong folks from getting in or out. In other words, Clark's free rein was probably a bit of a stretch.

That didn't make it any less captivating to watch, but it's interesting to note.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.