I hear Thirst has been quite long in the making.

Park Chan-wook: Well, although I say that this has been a film 10 years in the making, I've not necessarily spent all those 10 years making the film of course! At the beginning I didn't think of it as something very serious, I didn't give it that much of a thought. One night I thought of the idea of a vampire film and wrote it down on a couple of bits of paper.

The idea that I had at the time was of a priest who was also a medical doctor. He started as a priest, who went on to study medicine, and so has a licence to practice as a medical practitioner. So as a priest/doctor, he volunteers to participate in this biological experiment in order to help save humanity, but despite his good intentions he becomes a vampire.

That was the idea written down back then, but everything in the middle was a big blank. Somehow he would fall in love with a woman, after she realises he's a vampire and thinks he's a monster, he ends up taking her life, but turns her into a vampire. So these two ideas were written down way back then, and afterwards I was constantly struggling with how to fill out the rest of the story, but I went on to other more pressing films that I had been working on in that time.

What was it that fascinated you about the idea of a priest who becomes a vampire?

PC: It's because of the differences between the characters. Here is one identity which, by its very existence, can be looked at as evil: A vampire, who takes other peoples' blood in order to survive. On the other hand is this priest, which by the very meaning of the vocation is a vocation where you devote your life to others, living your life in service of others. Between these two identities, there is a huge ethical gap; a huge moral chasm. You have the moral height of being this noble priest, and the moral downfall to where you become a vampire, taking others blood. It's such a height to make such a fall. And on the way down there are bigger scares and more thrills that you have to go to, that there is a bigger sense of vertigo that you feel.

Did you struggle with the conflict, taking the character too far one way or the other?

PC: They are actually inseparable, the identity of a priest and the identity of a vampire, so I didn't have any concern about which extreme to take this character at all, because they had to co-exist. He is a priest who is forced to live on as a vampire despite his faith. This conflict, the suffering, and the pain that he goes through; this struggle is the main point of this film so the two need to go hand in hand.

Let's say I'm shooting a sequence about Beethoven, on the first performance of his ninth symphony, and when the concert finishes, and there is a roar of applause from the audience, but he can't hear and he's facing away from the audience, so one of the orchestra members has to turn him around to face the audience and take his bow. If I was to shoot this sequence, would you ask whether this was about the man with a hearing problem, or about a great composer? These two matters go hand in hand. If it hadn't been about the man having a hearing disability, would we even shoot the sequence?

Still from Thirst.

In casting the female character Tae-joo, what considerations do you have to make about how she'll play off Song Kang-ho?

PC: Complexity, instability, and somebody who can cover all the different stages that this character has to go through, from almost child-like innocence to a downtrodden housewife who is burdened with all these chores and having to deal with everyday life situations. In this film, it almost feels as if her clock is running in reverse. She starts off as a downtrodden housewife, and then she turns into a young woman in love, and then when she becomes a vampire, there is this dialogue saying, "Happy birthday," and this is where she is turned into almost a child, a baby.

So I needed somebody who could handle all the performances for all these different states of the character, and could deal with all these different ages that this character goes through, so she needed the right appearance for that as well as the acting chops required.

Oh, and lastly, sex appeal.

Did you see all that immediately in Kim Ok-bin?

PC: Yes. Even within five minutes of first seeing her, she exuded all those qualities that I needed, and I saw just how energetic she was.

You've directed some quite disparate films. Are there any constants for you, as a director, which you feel apply to your body of work as a whole?

PC: Yes, I feel there are constants throughout by body of work. Dealing with absurdity and dealing with surrealistic expressions.