The 'Final Girl' Theory.

The ‘final girl’ is a thriller and horror film (particularly slasher film) trope that specifically refers to the last woman or girl alive to confront the killer, supposedly the one left to tell the story. The final girl has been identified in many horror films, including Halloween, Scream, The Texas Chain Saw Massacre, I Know What You Did Last Summer and Alien. The term was invented by Carol J. Clover in her book Men, Women, and Chainsaws: Gender in the Modern Horror Film. Clover suggests that in these films, the viewer begins by sharing the perspective of the killer, but experiences a shift in identification to the final girl partway through the film. 

According to Clover, the final girl is typically a virgin, avoiding the ‘sins’ of victims - an example of this would be having sex. The final girl would usually have a unisex name (e.g. Teddy, Billie, Georgie, Sidney). 

Occasionally the Final Girl will have a shared history with the killer. For example, in Halloween II, Michael Myers is revealed to be the brother of Laurie Strode. In Scream 3 the killer is revealed to be Roman Bridger, half-brother of sole survivor Sidney Prescott. In the very first Scream, ‘Ghostface’ is actually Sidney’s boyfriend whose father was having sex with her mother before her death. The final girl is the ‘investigating consciousness’ of the film, moving the narrative forward and as such, she exhibits intelligence, curiosity, and vigilance.

One of the basic premises of Clover’s theory is that audience identification is unstable and fluid across gender lines, particularly in the case of the slasher film. During the final girl’s confrontation with the killer, Clover argues, she becomes masculinized through 'phallic appropriation' by taking up a weapon, such as a knife or chainsaw, against the killer. 

Clover also points out that the villain of slasher films is often a character whose masculinity, and sexuality are in crisis. For example, Norman Bates in Alfred Hitchcock's Psycho. Clover points to this gender fluidity as demonstrating the impact of feminism in popular culture.

An interesting feature of the genre is the 'punishment' of beauty and sexual availability. The idea of Sex = Death. 

The director Wes Craven (who directed Scream and Nightmare on Elm Street), played on the role of a 'final girl'. In Scream 3, Sidney, Dewey and Gale are presented watching Randy's 'Surviving A Horror Movie' video in the police station. Randy states that if you're in a trilogy or the concluding chapter, there are some changes:

- Anyone including the main character can die.

- The killer will be 'superhuman'.

- The past will come back to bite you.

- You can die if you're a virgin. 

Some information taken from:

http://en.wikipedia.org/wiki/Final_girl