Plot elements can be common. There are quite a few movies, and even commercials, throughout history that have the same type of storyline. This happens mainly because it’s human nature. Even if a plot line is close to another it is not consider to be a copyright violation. The idea behind why it’s not an infringement has to do with intent. Just because two movies or films are similar doesn’t mean they are in the same genre, or that they’re imitating one another on purpose. The overall idea is that each film has its own unique message and it’s a clear parody. This is how a lot of songs, jingles and movies are produced in two different genres such as drama and comedy. They do not directly take information and re-use it; they create new content based on a parody of it. Knowing all of this, it is still a good idea to ask an artist or film maker for their permission out of respect. It’s still different from stealing or plagiarising, even if it is more complex.