Another time, he might have lost himself in concentration on the work at hand.

They are found in very low concentrations, usually less than 5%.

He closed his eyes and looked to be in deep concentration.

She followed it with her head down, a study in concentration.

But the back was a study in concentration, or so it appeared.

But really, that look is the product of long years' training in concentration.

Its eyes had closed, apparently in concentration, some minutes ago.

Jesse is a study in concentration when he has a fish on.

And why does he have his eyes closed in such tight concentration?

He was deep in concentration, needing to make his point.