He didn't play cards himself, but was a keen observer.

What colorful stories from these keen observers of human nature.

A keen observer might wonder whether young people should be used by their schools in such a way.

He is also a keen independent observer on international relations.

But they became keen observers of both nature and human behavior.

He was a keen observer of economic trends, development and change.

A keen observer would have recognized two of the men as police officials.

He is a keen observer of the meaning that other people give to their lives.

As a keen observer of the human condition, I thought you saw through people better than that.

The Doctor, a keen observer, noticed the change in his voice, and determined to understand more.