A really fancy word for a blockhead. Those of us who tock our own heads when knocking on wood can relate. This is a rare one, rare enough one cannot be entirely sure that the form is actually xylocephalic -- but the one above sounds better, to my ear. But then, maybe that's also wooden. Coined from Greek roots xulon, wood + kephale, head.
Why no, you xylocephalous murid, we shall do the same thing we do every night -- try to take over the world!