I sat staring at the hundred dollar bill, with my mouth open.

He'd just sat there with his mouth open, unable to think of any story at all.

The poor chemist sat with his mouth a little open.

Still, he said, "You just kind of sit there with your mouth open where the cuts are going to be."

I was sitting there with my mouth open, wondering what made the guy tick.

"I used to sit there with my mouth open, wondering what would happen next."

Now she sat with her mouth open, shocked at the story he'd blurted out.

What I needed then was to sit there with my mouth open and think for several minutes.

North had been sitting with his mouth open and an expression of outraged alarm.

The result was that he forgot what he'd been about to say, and sat with his mouth open a moment.