I am using Lynda's video tutorials as well. I am also having a problem with the boolean operation at this stage. I have created the "box" for the mouth, positioned it in the body, but I go to Edit NURBs -> Booleans -> Union Tool, select the body, hit enter, select the rectangle, and hit enter, and Maya says:
Error: explodeNurbsShell8 (Explode Nurbs Shell Node): Not a valid NURBS shell.
I have tried selecting things in different order, etc., but it just doesn't work. Any ideas?