How would you show them that using the HTML source?

You can use dev tools to view the network tab to find whatever URL Pandora is using.

You can use dev tools to find a media elements src attribute.

To see the JavaScript sources... You check the dev tools.

If anything, in the days of JavaScript, the HTML source will missing a few things.

If there's an audio tag, that element exists in the DOM and has a reference to the url where you can download it. Is this a trick question?

Yes, my mother doesn't know what DOM is or why there are so many buttons in devtools. ctrl+u -> ctrl+f -> mp3 is much easier to explain and repeat.

Right but then you're talking about viewing the HTML source right? In other words "View Source." I'm asking why dev tools would need access to the original source and not the DOM. It doesn't make sense to save the original source in memory to me once it's been parsed.

ctrl+shift+i, ctrl+f "mp4"