This Robotis Third Arm is partially Autonomous. They can move in whichever direction they want which depends on the partner's movement
For safety reason, the arm stops at 10cm away from you, in case of causing any physical damage.
Coming to the facial expression part, You will have to make your Frowny face and letting the robot know that the food picked is just not your kind.
What are you waiting for?? Build your own now. You can use the microcontroller for controlling the servo which you have learnt in Expert level.
source: IEE Spectrum