Why did the director Kelly put the phrase "Deus Ex Machina" in the film? Why does Donnie say "Deus Ex Machina?"

from Movie FAQ – Donnie Darko on Rap Genius

Meaning

Deus Ex Machina is an unexpected power or event saving a hopeless situation, esp. as a plot device in a play or novel.

Director Richard Kelly put the phrase in the film to show that there was some kind of advanced machine someplace in the future at work, manipulating people and sending signals to Donnie in Middlesex.

http://www.youtube.com/watch?v=BV60298kBIk

When Donnie mentions this in the film he comes to realize that there really is a Deus Ex Machina. Donnie mutters, Deus Ex Machina, our saviour as a car driven by Frank stops nearby, which startles his attackers and causes them to flee.

The car acts as the deus ex machina; that is, the unexpected or unprobable device that is introduced to resolve a problem, thus it is Donnie’s saviour.

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