Perhaps, she said; and then swiftly passed out of the little glade, leaving John standing there as though he had been turned to stone. 
John wasn't literally turned to stone, but was acting like he was.
John was literally turned to stone. He saw a Medusa.
There was a possibility that it was the case, but it wasn't very important to figure it out, and to do so would have been to waste time solving idle puzzles.
A woman walks along a sidewalk next to a tree.
It is very clear to me what you are saying.
They did a drug raid that upset the whole town.
McGwire hit a foul ball.
In the event that I had revealed my ideas to you, Mr. Alfred would have been absolutely oblivious to your knowledge of my ideas.