To mute is human, to unmute divine.

Today's mission proved to be a great insight into the (perhaps unexpected and unrealised) challenges facing user interface software designers, in that it transpired Mrs S's issues over her muted microphone on FaceTime arose from how she interpreted the crossed out microphone symbol at the bottom of the screen and what the changing colour of the symbol meant (even if the crossed out line through the microphone never actually disappeared...) - and how many times to press the mouse button to "unmute".

Hopefully my explanation, a few test runs to show that the microphone was working over FaceTime when the microphone symbol was grey (as opposed to white), and hand written quick reference page come in handy for Mrs S going forward when she next uses FaceTime to call her family.