Yesterday I was looking up this interesting CSS 2 property called background-attachment.
Its no big bang. It can have a couple of values scroll and fixed. Scroll will scroll the background image with the page and is the default for all elements that have a background image specified, Fixed will make the background image stay in the same position even when the page is scrolled.But with a few tricks combined with the background-position property, this can be leveraged to give neat little animation effects when the page is scrolled.
I notched up a small demo with a couple of paintbrush illustrations and tried to give the effect of filling a glass with water. Those interested may fill it with Beer or whatever they like. 😉