DD has a little cubby hole in her room in the eaves in which she has cushions and some little lights strung up. Last night she was looking for some new batteries for the lights as they were dimming. But we couldn't find any.
This morning when she went in her cubby hole, the back of her mouse had been removed and its batteries were sitting next to it. 
DS was asleep when DD was looking for the batteries and didn't go in her room in the morning before school, so it wasn't him. DH was out and didn't know we'd been looking for batteries. I didn't do it. There hasn't been anyone else in the house.
I'm sure Jonathan Creek would have an explanation, but any ideas?