Sentence:  Looking in the same direction, I saw that the <WSD>knothole</WSD> in the wall had indeed become a human eye -- a full, black eye, that glared into my own with an entire lack of expression more awful than the most devilish glitter. 
Meaning of the word marked with <WSD> tags:  In a piece of lumber, a void left by a knot in the wood; such holes are often convenient for peering through when they occur in fences.