Caskett Kiss Theories Anyone???

OMG!!! I just saw the promo for the long awaited 3x13 episode and I know I'm not the only one excited about the kiss between Castle and Beckett!! I'm dying to know what's behind it though because in an article I read it said there's more to it than passion so I was wondering if anyone has any good theories that have to do with the kiss because I've got nothing lol. In the promo it showed them standing REALLY close and Beckett is laughing and then Castle just goes in for the kiss so I'm thinking that she'll be thrown off guard and I'm dying to see what her reaction will be since she's still in a relationship unlike Castle! Sorry this was so long and please share any theories and/or comments about the upcoming episode! Thank you! :)