A stud in the sheath is used to unlock the blade for sliding it shut and for sliding it open. Its not terribly easy to explain, thus:
Old style clip, new sheath offers better protection
http://www.youtube.com/watch?v=H7LGxVzrGCc&feature=related
http://www.youtube.com/watch?v=Nuo2CEyLtBk&feature=related
AUS-6 is the blade steel on the Chubby.