He didn't need to turn to know what was happening behind him.

He did not know what was happening behind his back.

"The city will never put what happened behind it," he says.

Much, however, already had and was to happen behind the scenes.

And then she was running, afraid of what might be happening behind her.

She takes care of the things that happen behind the scenes.

He was conscious, but everything around him happened behind a wall of glass.

I saw what really happened behind the walls of the prison.

However, it is a knowledge of what happens behind the program that makes all the difference in whether a page looks good or not.

What happened behind that bedroom door was no one's business.