Memes are ideas, behaviors, or styles that spread from one person to another within a culture through writing, speech, gestures or other imitable forms of communication. They act as units that carry cultural ideas, symbols or practices and replicate, mutate, and respond to selective pressures like genes. Chuck Norris is an example of an American martial artist and actor who became a popular meme, with his name often followed by jokes in the same way as Indian actor Rajnikanth, where merely mentioning their name implies something funny.