I was thus faced with one of two alternatives—either someone had used my boots in the night to effect this change in the tunnel, or I myself had walked in my sleep to bring it about. And I could not much doubt which it had been—for, despite my eagerness and anticipation, I was fatigued in a way which would have been accounted for only by my having spent a considerable portion of my sleeping hours digging away at this blockade in the passageway.