In the episode: "One more for the road", you see Carol and Doug discussing Charlie (the 14 year old drug-addict) over phoning and chart-reviewing. Carol is standing beside Doug.

Suddenly somebody calls from behind the desk. It's Tommy, a "friend" of Charlie. When he's in the picture, you see Carol sitting in a chair, instead of standing. If she had moved to the chair, she must have done that SO fast, it's impossible!

I usually don't like finding mistakes, but this one is just funny.