Hes saying, if you model a box.. its going to be hollow, as there are 6 polygons. Lets just say you put another box above that... it technically now has thickness. So if you modelled a cylinder and chopped off the top, it would look quite thin.. if you extruded inwards and made a barrel.. you would have thickness to your object . So if you took your geometry there, and duplicated it. and then scaled it bigger or smaller, you could then join the edges and have a (thick) jaw .. hope that makes sence. BTW, do you have an alienware computer... or if not, which skin are you using for windows? Thanks . If you still dont understand.. then let me know and i will make you some images to explain ok?