This picture shows the completed circuit after finished the code, before assembling with the cat toy. 

Outcome:

To assemble the prototype, I attached the cat toy, a stick and string assembly, to the servo motor. I mounted the servo and the sensor/toilet roll assembly to a bookshelf. After initial testing, I realized that the sensor would have to be pointed out of range of the moving cat toy, otherwise it would continue on forever. I moved the sensor assembly to the wall. Once everything was attached, it worked great. 

Marcel was initially intrigued by the moving string, but I think he was also a little startled by the jerky movement and sound of the servo. I could keep working on a servo movement sequence that most appealed to him. See pictures and video below!

(Continue scrolling to find Reflections and Sources)