Power, Makey Makey, Servo. I also used the servo mount.
The second step was to build a conductible strip to attach to the door. I used tin foil, alligator clips, and wire.
The third step was to complete the Makey Makey circuit. I attached tin foil to the door stopper so when the door was opened it would release the dog.
The fourth and final step was to make the servo take the nail out of the crate. I used a twist tie to attach the nail to the servo and some tape and the servo mount to keep the servo in place.