knit (one's) brow(s)
To furrow one's brow, often due to worry or confusion. Whenever there was a problem, my dad would sit in his favorite chair, knit his brow for a while, and then announce that he had a plan. When I asked Bill about what happened, and he knit his brows, I knew I was about to hear some bad news.
knit one's brow
to cause one's brow to wrinkle. Bob knitted his brow when he was confused. Jane knitted her brow because she was angry.