When you treat history like a science, or when you're doing a historical science (like geology), things that are out of place in time are important pieces of data. Things that are out of place in time are known as anachronisms. This would be like finding fossil cows mixed in with a herd of dinosaurs. You just never find those things together at the same time. And you'd never find disco music in the soundtrack of a movie made in the 50s.
Of course anachronisms can play a significant part of a movie. Mel Brooks' movie Blazing Saddles wouldn't be nearly as funny if it didn't have a sheriff in a Gucci outfit and the running gag of “Hedy Lamarr”. You can also through aliens into a western, or move a story about knights onto another world. The movie Avatar was just the western, Dances with Wolves, moved to an alien planet.
In movies and plays we usually use anachronistic language since we want the audiences to understand the show. But sometimes we make the language just a bit off to give the show the impression of another time and place. There's a lot that can be done by just using a more formal language. But different times and place have had different cultures, and throwing in some anachronisms can make the situation more easily understood.
Tehachapi Community Theatre's upcoming play The Lion in Winter, has a large number of anachronisms. Some of these are intentionally put in to give the audience a frame of reference. Fore example, the Christmas tree. Others are unintentional. Such as the mention of “poison oak”.
The play takes place in Chinon France in 1183, where King Henry II of England has called together a Christmas court. All the characters are historical, though all are also fictionalized.
The play shows the maneuvering between the king and queen, their three sons, and the young French king and his sister, all trying to affect the future of England. Both dramatic and funny we watch as each of them make what they think is a winning move, only to find themselves not in the winning position they thought they had.
So come out and see the show. Watch for the anachronisms. Pick a side and hope they come out on top.