Animated rollover-length of time effect

hello folks,

I’m curious how these folks did these type of rollovers found on the navigation of the following sites:
find the main site navigation and click on the “see solutions” button. It should drop down to other sub navigation items. What I’m refering to is the rollover animation effect in the sub nave items.

also the main navigation found here:

What I find interesting about this is how the rollovers seem to get hotter or smokier the longer the mouse stays over the button. How is this effect achieved?

Thanks for any help you could lend.