Sentence:  He looked at her out of himself , she thought , as he did only for an instant at a time , the look which always surprised her even now when his uncombable hair was yellowing a little and his breath came hard through his <WSD>nicotine</WSD> choked lungs , the look of the gaunt youth she had suddenly found herself staring at in the Tate Gallery on a Thursday once . 
Meaning of the word marked with <WSD> tags:  an alkaloid poison that occurs in tobacco; used in medicine and as an insecticide