The “only thing” left in the house was the toilet brush!
Did they mean to leave it as a housewarming gift for the new owners, a kind thought but a used toilet brush would not be high on anyone’s points list.
But if you leave gift where is the best place you leave it? Usually the kitchen counter would be the choice area for gifts, with a nice card wishing them well in their new home, but a used toilet brush needed more thought, they probably tried beside each of the three toilets in the house before finding the ideal location, the shower. It would have been placed on the right side, left side, in the middle, rotated for the best presentation and finally making a unanimous decision by all the family to place it in the left rear corner of the shower. Success, happy, done.
One can only imagine their sense of accomplishment having made their decision as they stood in the bathroom doorway together, looking at the toilet brush carefully positioned in the corner of the shower where it would be immediately spotted by the new homeowners when they move in.
Or were they downsizing and no longer had space for the toilet brush and no idea what what to do with it. The moving company packers asking them if they wanted it boxed up and shipped with everything else, as they drank their last coffee and made the decision to gift that one well used prized item in the house.
Surly it was not forgotten, it was way too obvious where it was, we will never know, but it is funny what people choose to leave behind when they move out of their home and leave it ready for the new owners.