Intertextuality is the shaping of a text's meaning by another text. It is the interconnection between similar or related works of literature that reflect and influence an audience's interpretation of the text. (wiki def)
The three types of intertextuality are obligatory, optional and accidental.
Obligatory Intertextuality is when the writer deliberately invokes a comparison or association between two (or more) texts.(Wiki)
Optional Intertextuality means it is possible to find a connection to multiple texts of a single phrase, or no connection at all.(Wiki)
Accidental Intertextuality is is when readers often connect a text with another text, cultural practice or a personal experience, without there being any tangible anchorpoint within the original text. (Basic Knowledge 1o1)
Fiona is seen with a wedding ring falling on her finger which also happens in the lord of the rings.
in this image the Simpsons copy the Beatles album cover
In this image the character Rex is seen in the reflection of the toy car parodying the scene in Jurasic park where the Tyrannosaurus Rex is seen in the reflection of the car.