Sentence:  They trod noiselessly upon a stair carpet that its own loom would have forsworn. It seemed to have become vegetable; to have degenerated in that rank, sunless air to lush lichen or spreading moss that grew in patches to the staircase and was <WSD>viscid</WSD> under the foot like organic matter. 
Meaning of the word marked with <WSD> tags:  Sticky, slimy, or glutinous.