Hello,
Maya 2012 question - student version
I have been working on making a face and was following slorpthegillman’s tutorial on youtube (ran into the problem in part two of the series if you want to see the steps and stuff, around 6:30) and when I select the edges around the opening of the mouth and extrude those edges, some of the faces of my model disappear. I can still ‘select’ them when I ‘right click’>‘faces’ but they aren’t visable. Here is a picture so you can see what I’m talking about.

As you can see, a lot of the model is fine, but some of the faces are missing 
Perhaps I am missing something/forgetting a step? I’m on a mac, maya 2012 student version.
Thanks so much in advance!
Sissyharu