We also have a cat door cut out in the door that leads to the basement. My cats' food and litter boxes are kept down there because of course my dog would also like to eat their food. The only part of my dog that fits through the flap is her head. Sometimes when I am coming up the steps, Bella has her head through the flap looking down at me and she looks just like those deer heads that people often mount on walls! I should really get a picture of that some day. Too funny!