In concept, this is fairly simple. Lift the tag and light strikes a photocell--triggering the action. The sound module plays a prerecorded "Eeek" and the package backs up, turns and takes off. The Arduino/Motor Shield monitors current going to the motors. When the package strikes an object, one or both motors struggle to operate and draw an increased amount of current. The increase in current lets the Arduino know it is time to play the "Eeek," then back up, turn and take off. This continues until the master toggle switch is turned off.
Add "+" from the recording module to the top of the relay/1n4004 diode.
Remove the passenger compartment of the car.
Separate the bottom of the car from the top by removing the screws in the base.
Cut the wires to the receiver module and save the module for a future project.
Drill holes in the battery compartment and bring the motor wires through those holes.
Solder extension wires to the motor wires. I use heat shrinkable tubing to secure the connection.
Take the printed "screaming base" (see Thingiverse -- or make one from plywood) and route the wires through the center.
Secure the base to the wheel platform with screws.