How are they determining what is a "Hot" thread vs a non-Hot thread? I've seen some with view counts and reply counts at similar levels yet one would be deemed Hot and another, not so much. Just curious as to their process?

I took a quick look through the FAQ but I didn't find anything.. of course it could be that I wasn't looking very hard, so I apologize in advance if anyone is about to point out something extremely obvious to me.