Flo has a habit of catching various animals, dragging them inside through the cat door, and letting them loose so they can be chased for hours. To put an end to this we have built a computer-controlled device that visually determines if Flo is carrying anything in her mouth when she enters, and if she does, it simply does not let her in.

http://www.quantumpicture.com/Flo_Control/flo_control.htm