fall open
come open

Her mouth fell open but no sound would come out.

Her mouth fell open when she saw what they were.

My mother's mouth fell open and she held out her hands.

I got out of bed, and nearly falling opened the door.

What could we do when the border suddenly fell open?

Her mouth fell open, she had no idea in what shape.

His mouth fell open, but the words were a few seconds behind.

Sam stopped talking for a moment, then his mouth fell open.

His mouth fell open and he nearly dropped our dinner.

He turned pages until they fell open to the S's.

And even as he said it, his mouth fell open with wonder.

For a moment he simply stared, then his mouth fell open.

As she did, her mouth almost fell open from the shock.

Betty's face fell open and the General couldn't find anything to say.

The book fell open to a page with two photographs on it.

He took the folder and let it fall open in his hands.

The first time he did that, my jaw fell open.

Her mouth fell open, as though the lower jaw had died.

The book had a propensity to fall open at one particular place.

A safe just happened to fall open when I was passing and the report dropped out.

The pages fell open to the middle of the volume.

On the desk, the book had fallen open at a certain page.

Then she saw the implication, and her mouth fell open.

He turned to the nearest man, whose mouth fell open.

When the bag fell open, the whole place felt warmer.