Adywan, although I've always been more than happy with the 'movement', 'scale', and 'debris' that the Space Slug 'puppet' currently conveys as it emerges, there is a little something that always catches my eye during the shot - http://www.theforce.net/swtc/Pix/dvd/ep5/sslug3.jpg
When the Space Slug is fully emerged (as seen in the link), we see some kind of thin 'elastic'-like piece on it's left-hand side 'twanging' against it, near the 'cave' opening. While I don't know if this is meant to be a 'fold of skin' or something, I reckon it would be better (and less distracting) if this was erased.