The moment Beckett turned off the car, Castle was already smiling with a combination of 'damn i'm good' and 'triumphant victory'. The result was a smirk to die for. Of course, he tried his best to hold it at bay until Kate was close enough to him for him to wrap his arms around her. Hugs are always great. Especially when there are ulterior motives involved.
"This moment is going to last forever." is whispered to Beckett, in the midst of Castle very likely hugging too tightly. It's only happening like that because Castle needs to keep a grip on her for...
Surprise! What looks like a random passerby whirls around and holds up a digital camera with the epic quickness! Photo Taken!