I'm gonna skin the, uh... throbber

in SkS. I know what it is, but I've got no idea how to skin it, and SkS ain't forthcoming with the info, being an unsupported feature.
So... there are 3 image sizes: large, medium and small. Are these avi's or tiled images? What are the dimensions per frame? Are there a specific number of frames to throb?
Does anyone know?
Does anyone care?
Are we alone in the universe?
Eternal gratitude and maximum respect to anyone who can answer at least the first set of questions...