Casting.

If you were making a movie about a small Southern town, and you needed to find an actor to play Cousin Larry what would you do?  Now Cousin Larry is a little slow. He finds it hard to put his thoughts together, at least when he has them. He walks around in a kind of permanent daze, his mouth always partially open as if he were going to say something important, but he never does. He always looks like he just woke up from a long nap and can't quite connect with the waking world.  True, it's not a pivotal role to the movie. Still you would probably need someone to play Cousin Larry who wouldn't be good at playing anything else.