I wanted his eye to rotate when someone takes his cap off. To implement it, I found electronic modules as pic 2.
1. Seeeduino (an Arduino compatible microcontroller) 2. Base Shield (an extension board for Grove modules to connect to Seeeduino) 3. Half ping pong ball (I got it by cutting through a ping pong ball, but you can also find some other doom thing to replace it) 4. Grove - Servo (create the rotation of the eye) 5. Grove - Light Sensor (detect if the cap still lays on Mike's head)