In an interview with Star News, when Park Shin Hye was asked about the obvious chemistry between her and Lee Jong Suk in Pinocchio, she had a surprising response as to why the couple interacted so convincingly on the set.

About her relationship with Lee Jong Suk, Park Shin Hye commented, "I fought a lot with Lee Jong Suk. He is very straightforward. If you're pretty, he would say, 'You're pretty,' if you're weird, then he'd say you're weird. If you're ugly, then he says, 'You're ugly.' He is exact like that. We did monitor each other a lot, and rather than coaching each other on our mistakes, we would ask each other, 'Was I weird?' or 'Was I stuttering?' and answer [honestly]." 

While this may seem like rather abrupt behavior from Lee Jong Suk, it actually shows that he really cares about the success of Park Shin Hye and her growth as an actor. It seems like he is also humble enough to take constructive criticism in return.

Even if there was not a real love connection between the actors, it sounds like they have a great relationship. I hope they work together again in the near future!

To see their chemistry in action, you can watch all of Pinocchio now!