Knit (one's) brow(s) American British verb phrase
To draw one's brow together for being worry or thinking carefully
If any disputes arise in the meeting, John will find a ventilating space, knit his brow for a while, and then come back to continue.
When Jane's parents asked him about the exam, he shook his head, knitted his brows, and went straight to his room.
My mom keeps knitting her brows when witnessing the toddle of the grandchild.
The verb "knit" should be conjugated according to its tense.