Hot Glue servo horn onto the back of each eye and attach to a servo motor.
Make sure you mount one when the motor is fully rotated and the other when the motor is not rotated and the two motors will rotate in opposite directions to achieve the desired effect. This is always adjustable later.
Attach to an arduino to make the robot. It is easy and tweakable to make the robot respond to different inputs. In this case I used a light sensor to detect light, but any input is easy. Here is the sample code and the layout used including the light sensor http://123d.circuits.io/circuits/403016-robot-eyes
In my case, I have to not forget to give the plant plenty of light!