Mirror image.

It was not uncommon for Dad to emphasize his point with a raised eyebrow. It is one of the expressions I miss most.

I, too, can (and often do) raise one brow while lowering the other. My expression mirrors Dad's: he raised his right eyebrow; I raise my left. I have tried to raise my right brow, but I cannot.

A few days ago, I gave my son the raised eyebrow. To my surprise, his right brow shot up in answer.

For an instant, I saw the reflection of his Poppa. Just as I mirrored my father, my son mirrors me.