The term 'follow furtively' can be summarized by two crossword solutions: 'STALK' (5 letters) and 'TAIL' (4 letters). Stalking is the act of following someone without their knowledge or consent, usually with malicious intent. Tailing is similar to stalking, but it is done with the intention of keeping track of someone's movements. Both terms imply that the person being followed is unaware of the activity.