Thank you L5730!!!
I have discovered (with your help) that the following works:
/Applications/VLC.app/Contents/MacOS/VLC -I rc video-and-audio.mp4 --no-sout-video --sout-audio --sout "#transcode{acodec=mp3,ab=128}:std{access=file,mux=raw,dst=just-the audio.mp3}"