Boolean Difference Tool Not Changing Shape So I'm designing the head model for a video game character, and my boolean tool stopped working.

I'm trying to subtract two UV Mesh Spheres from a complex shape in order to create eye sockets like so:



When I overlap the shapes and try to do the Boolean Difference, for some reason it does not subtract the sphere from the face of the object (lets call it "skull"), but half of the sphere still exists inside the shape (what would be the back of the eye socket).



Can someone please show me how to fix this? It's really slowing down my project, and I don't want to start playing with the vertices. 

Thanks
-K
I don't have enough reputation to comment but looking at the blend file you posted, it looks like the normals on both objects are flipped inside out. Using "Make Normals Consistent" on both meshes seems to make it work okay.

You said you already did this, though. Perhaps the "Inside" checkbox is checked for you? I didn't see that in the blend file you posted though so I'm not really sure. But the skull mesh in your screenshots and both the meshes in the blend file you posted are definitely inside out, you can tell from the weird purple black thing they've got going on.