In the next snippet we expand on a point by providing more descriptive detail. Notice the way the thing is repeated on both sides of the em dash.
At times I felt like I was failing Maureen, like I wasn't keeping my promise that I'd protect her—the promise I'd made to her when I held her on the way home from the hospital after she'd been born.
Dad drove us to the pier—the same pier where we had caught the shark almost one year earlier.
I bought a banana—a banana so big and yellow that it looked a cartoon fruit.
On my way to school I trod on a nail—a nail so big and rusty that it punched into the sole of my shoe, straight through my foot, and out the top of my Clarks.
On the weekend Bill and Bob showed a German film—an old one that was in black and white, with subtitles and lots of cheap ghosts.
