Why is there a crease in my mesh when I enable subdivision surface? I have a dinosaur mesh (more or less thanks to this).  Around the 11:55 mark or so, he shift+d's the toe from one side of the foot to the other.  However, I observe that whenever I turn on subdivision surface, there is a strange crease in the mesh.



What did I do wrong to cause this crease?  What can I do to get rid of it?

Thanks alot!  Blend is here.
You have inner faces, delete them and it will work: