The new microphone symbol on the bottom center of the Avatar screen indicates that the Avatar is listening to you. Whenever you see the symbol, you can say something to the Avatar and it trys to understand and respond.
Attention: Keep in mind, it also means, that the Google Speech to Text service is active.
As this is indicating the activeness of the Speech to Text service, it is activated or deactivated by the Avatars STT toggle in the robot's section:
Now you can see, what the Avatar has understood
Another benefit is, that you can see now, what the Avatar has understood and even what the Avatar is saying in response:
