Thanks Kurt,
I solved the problem by turning on polygon border edges and seeing that whenever I extrude an edge (on a Mac in Maya 6), the extruded edge is a border edge. I experimented with...

I'm in FrogPart3_final, about 4:00 minutes in, and after extruding my edges and scaling them to close up the wrist before attaching the fingers, I am unable like the video to delete the "extra"...