Alert regular Tim Servo writes:

I am constantly seeing familiar faces in real, actual movies of actors that appear in movies I see on MST3K.? Today I watched the 1956 serious movie “Julius Caeser” and one of the Roman senator-type guys was the sort of German scientist from “LOST CONTINENT.”

Oh, yeah, this is happening all the time. It even happens on the show. On several occasions we got riffs like “Oh goody! This guy!” or “Hey, it’s THAT guy!”
According to Daddy-O, there are more than 7,000 credited performances in 200 or so MST3K movies, so you’re bound to run across some of them doing other stuff.
Recently I was watching “The Baroness and the Butler” on TCM and a very familiar face came on the screen.

It was actor Maurice Cass (I learned after looking him up) better known to us as Professor Newton on the “Rocky Jones” episodes.
So, Tim Servo wanted to get into a whole “seven degrees of connection” thing, but I think that’d be too complicated.
But I DID want to get into the “that guy” phenomenon. Have you had a “that guy” (or gal) moment with somebody in an MSTed movie? Who’s your favorite “that guy”?
Me, I’d have to go with George Cisar:
who was in the movie in episode 406- ATTACK OF THE GIANT LEECHES and is best remembered as “the doughy guy” in the movie in episode 522- TEEN-AGE CRIME WAVE.
What about you?