Masterful use of the passive voice

As I walked up to the bus stop this afternoon, I noticed that P was wearing her coat, yes, and snow pants, and hat and mittens … but not something else she left the house with this morning.

“Oh, Abba,” she said brightly as I approached. “My backpack was left at school.”

“Was left at.” I can’t tell if it’s my inner copy editor, my outer parent–or realistically, both of them in chorus–that had me put my head in my hands and groan.