Sentence:  If you were bold enough to ask Antonin Scalia questions, you had to be precise. Otherwise the bushy black brows would <WSD>furrow</WSD>, the chin would crumple and the pudgy, puckish body would start to rock, eager to get at you. 
Meaning of the word marked with <WSD> tags:  To pull one's brows or eyebrows together due to concentration, worry, etc.