Several weeks ago, my sister came and watched Mom while I went to my spinning group. A few days later, I finally noticed this.
I had to call my sister to ask if she had done it, or if Mom had. First, we had a good laugh that it took me so long to finally notice it. Then she admitted that she had done it. Turns out, her seven year old does this often. He'll leave his dinosaurs or monsters in the fridge for my sister to find. Like grandmother like grandson.