Oldboy (Original Korean Version)

So I just saw this movie for the first time, and I loved it. However, I had a question about one particular scene and I couldn't get a good answer while googling it.



Can someone help explain this scene? This just seemed a little odd. It looked like a freeze frame, but the other guy was slowly trying to reach for his own weapon. I didn't really understand the dotted line, either. Just wondering if anybody had an explanation.