Intertexuality basically means a film borrowing an idea from another film, and you might realise that some films may have similar camera angles, use of mise en scene and sound. One example could be a numerous number of films using ideas of the shower scene from the successful known film 'Psycho'.
What i love about intertexuality is that lots of film directors have copied the idea of famous brilliant movies scenes but have changed it to their content and made it more successful and more effective to the audience and in the way they use the idea.
Now let me get into more depth of why Psycho was used to much. The film was very famous for its shower scene in which it conveys horror and voilence, without showing a great amount of detail. When the unfortunate victim inside the shower falls after being stabbed, the shower curtain rail unhooks from the railing which is greatly used in many films.
Another example where intertexuality is used is in the great film 'Stepfather' where the stepfather is stabbed brutally in the neck and falls into the shower with the shower curtain rails being ripped off and falling in the bathtub with him. The similarity of both films is that when significantly injured characters would use any type of object for balance and support in order for them not to fall.