One amusing side effect of actors spending long hours together while waiting on sets in their down time is that they occasionally become familiar with each other's voice inflection and mannerisms. Being actors, with (hopefully) an existing flair for imitating fellow humans, many become adept at impersonating each other.
Some actors have more of a talent for it than others — for instance, Kevin Spacey is widely acknowledged to be great at practically flawless imitations. But who knew that Bradley Cooper could do a few pretty good ones? His Owen Wilson is good. His Walken isn't bad either. See all seventeen imitations by various actors at Esquire.