Intertextuality in film, is when films or movies use ideas or scenes from other movies in their own film!
...also known as....copying =D
Another example is the film 'Clueless' directed by Amy Heckering is loosely based on the novel named 'Emma' by Jane Austin.
In the world of thriller, one of the most 'thrilling' scenes of all time is used countless times in many films all over the world, this of course it the famous 'shower' scene from Alfred Hitchcock's film 'Psycho.' Many films such as 'The stepfather' and 'What lies Beneath,' have a tense, suspenseful scene involving a shower, this scene has made its way across our screens for decades and has become a trade mark for thriller movies.