SBS released two behind-the-scenes videos for intense drama 'Three Days,' showing the awesome chemistry between Yoochun and Park Ha Sun.

The first one covers the scene in which Yoochun saves Park Ha Sun from a car.  The staff joked that Park Ha Sun saved Yoochun when it was supposed to be the other way around as she pulled him in when he grabbed her, shielding him from the car.  It also showed Park Ha Sun all smiles and laughing as she has fun on a playground set. 

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The second video shows a cute Yoochun having a hard time with the dialogue.  Park Ha Sun also reveals her ideal type, saying, "Someone who I think would stay silently by my side for a long time.  I think Han Tae Kyung [from 'Three Days']--not Yoochun," naming Yoochun's character.

Although Park Ha Sun may be serious on camera, she proved to be quite playful off camera.  Check out the videos below!