For ears and tail we use small hobby servos, so we need a board to control them the same way we control main servo. The internal firmware gets binary commands on UART bus and translate them to PWM signals.
We have a lot of progress on a software to. Right now we almost finish intergration of SOAR cognitive architecture into Sweetie.
The goal of the Soar project is to develop the fixed computational building blocks necessary for general intelligent agents – agents that can perform a wide range of tasks and encode, use, and learn all types of knowledge to realize the full range of cognitive capabilities found in humans, such as decision making, problem solving, planning, and natural language understanding.
It is old but still actual and mature framework for build the complex AI based behaviour.
You can find some examples here: https://www.youtube.com/watch?v=Z7KuIrjWws0
She will get a camera soon with NN based object recognition. Also she will able to react to voice commands.