They're pretty big. I think one of the original members died if I remember right. Basically it's using their bodies to do surreal/abstract art, and it is very cool. I saw them like ten or fifteen years ago or so, and would gladly go again if I could afford it.
For a better explanation though, you should really just do the Wiki thing:
http://en.wikipedia.org/wiki/Pilobol...nce_company%29
I didn't know until just now doing it, that they were named after a fungus!