1.   His brow furrowed.

2.   At that, your brow really furrowed.

3.   Brows furrowed.

4.   Brows furrow for a moment, then the light dawns.

5.   Brow furrowed.

6.   Her brow furrowed as she explained her new soft-hitting editorial policy.

7.   Her brow furrowed.

8.   His brow furrowed just the least bit.