He wanted to be able to observe the man's reaction.

"You want to observe his reaction when we walk by?"

It was really only a test, to observe her reaction.

That we all have a chance to observe his reactions.

Maybe he would learn something useful by observing her reactions.

The great dark eyes observed with intelligence the man's reaction to the transformation.

I, who was in court every day, observed their reactions with detachment.

He observed the quarterback's reaction when discussing a poor play.

She scrambled away from him before turning around to observe his reaction.

What they seemed to be doing was observing the man's reactions and those of his fellow prisoners.