During the filming of the hit Korean movie My Girlfriend Is An Agent, actress Kim Ha Neul, who plays the title role, kissed her co-star so hard, her lips bled.

She also fell off a horse while male lead Kang Ji Hwan tore a ligament in an ankle.

But the pain was not in vain: The movie, which opens here tomorrow, became a hit in South Korea.

It out-grossed Hollywood blockbusters such as Star Trek and X-Men Origins: Wolverine, attracting over four million moviegoers during its screening there from April to June and grossing 26.3 billion won (S$31.1 million) at the box office.

The romantic action-comedy is about Soo Ji (played by Kim), a high-level spy who has to hide that fact and ends up lying to boyfriend Jae Joon (Kang) constantly.

Sick and tired of her lies, he goes abroad to further his studies and returns as a rookie spy.

They end up working for different departments in the same spy agency. Dramatic and funny moments ensue when they meet on the job.

Kim, who has starred in popular movies and idol dramas such as My Tutor Friend (2003) and On Air (2008), talked about the kissing scene when she was in town last week to promote the movie.

The long-haired actress, who kept her shades on during the media conference at StJames Power Station because of a stye in her eye, told Life!: 'In the scene, the actor and I were supposed to be very passionate as we were very much in love.

'We kissed so hard that when we pulled apart, I saw blood on Kang's lips. I was so shocked. I kept asking him why there was blood on his lips.'

The 31-year-old added with a laugh: 'After a while, I realised I was the one bleeding because of the abrasion during kissing. There was a lot of commotion due to the blood. It was unforgettable.'

Besides her bleeding lips, she also hurt her leg after falling off a horse during training before filming began. She had to learn, among other things, how to ride the animal and a jet ski for her role.

She said: 'After I fell, my leg was in a cast for one month, so my training period was reduced to two months. The regrettable thing was that I had less time to train but my leg is fine now.'

And it seemed like her co-star had as tough a time.

The 32-year-old tore a ligament in his ankle during an action scene and had to stop filming for two weeks.

Kang said: 'As I still had many action scenes left, I had to continue filming although my ankle still hurt. I took painkillers and bandaged my ankle while filming.'

The soft-spoken star added: 'My ankle still hurts from time to time now, and frankly, I still feel nervous about filming action scenes.'

The on-screen chemistry between the two is palpable and the two leads are rumoured to be in a relationship.

Neither, though, would confirm it.

The movie is about deceiving the one you love and the two stars had different takes on what they would do if faced with the same situation.

Although her character lies to her boyfriend, Kim said trust and respect were the most important aspects of a relationship.

When asked which she would choose between love and career, she said: 'This is such a difficult question. I would choose love because it is hard to find someone you truly like and get into a relationship with him.'

Kang, however, said he would pick career.

The actor, who has starred in Korean idol dramas such as Be Strong, Geum Soon! (2005), laughed and said: 'If a man has a successful career, women will naturally fall for him.

'Without money, how do I get into a relationship? I think I will go for both - career first, and love second.'

So what does he look for in an ideal partner?

'Since I am an actor, I need an understanding girlfriend because there are many restrictions on my life,' he said.

'But because I've been single for such a long time, I don't mind any girl who likes me now.'

This is the first time he is visiting Singapore and he said he found it quiet, clean and comfortable.

'I feel like moving here to work because I feel so relaxed. I really like the feeling I get in Singapore.'

Kim, who has been here before to film a show, said she was happy and excited to meet her fans last week during a public appearance at The Heeren.

'I didn't know I had all these fans in Singapore, supporting me over the years. The next time I shoot an advertisement or movie, I will definitely keep them in mind and go overseas to visit them too.'

Kang added with a cheeky grin: 'From what I know, only mega stars like Bae Yong Jun have a fan club in Singapore.

'I would love to have a fan club here, too. If one is formed, I would support my fans and visit them often.'

jocelee@sph.com.sg

This article was first published in The Straits Times.