Oops!

I've been busting to go the loo for hours so, when the shop was empty I bolted the door, left a "back soon" sign on the door and raced out the back. (No inside toilets in these old places.) When I came back I could hear a voice plaintively calling out "hello, hello."
I'd locked someone in.
Fortunately, she was able to laugh about it.
I'll have to look more carefully for these silent people lurking in amongst the shelves!