Katy has many admirable properties, and as the owner of a dog that's too clever, her lack of insight is one of these. When she was very small, this stool on the steps prevented her from going up the stairs. Despite the fact that she could easily step over it, this stool is all that it takes to prevent her from going up the steps still. She watched in amazement as Corvis cleanly stepped over or around it, but didn't process what that implied about her own capabilities.