Some of them are internal searches. The parameters that happened to be in effect when g### visited the site are different from what's there when you go yourself to check up. Especially helpful if the site is, say, in Japanese and you have no idea where the Search is or what to enter to replicate the effect ;)
Also scroll-downs. The ones where you click for more links. Somehow they all show up in the SERPs even though the extra links aren't visible in the page code.
Those are just ones that I've personally seen.
There was a similar thread not long ago where someone said that g### doesn't even show you your really good links. Just the crap ones. So you're fundamentally wasting your time trying to investigate.