What episode do you think he starts falling for her?

I'm curious what you guys think, when does Spike's infatuation with Buffy start? When he first declared his love for her I kind of thought it was out of nowhere and weird. Although I did end up being a fan of their relationship and wish we got to see more of it.

Someone mentioned they thought it started when Faith swapped bodies with Buffy, and she saw Spike at The Bronze and made that very graphic comment to him.

I guess I missed the subtle signs of him starting to fall for her, and I kind of want to go back to those moments and rewatch, to see if I pick up on them now that I finished the series.

So what episodes do you guys think it starts?