I’ve heard that a lot, and I always thought it had to do with lazy talking (not moving your mouth much). I do think that’s part of it, and some people do that more than others.

But the thing about having a potato in your mouth is it pushes your tongue down and back, into your throat. Which is something you need to say the American “r” and a lot of other sounds, like “w” and the dark L like in “pull.” It’s hard to teach, and very hard to unlearn. It’s part of the characteristic American sound.

German is basically the opposite. You can see the difference here, with a German speaker talking in an MRI. There’s a lot of space between the back of the tongue and the back wall of the throat. And here’s a picture of someone saying an American “r”. The base of the tongue is all bunched up in the throat.

Yep. That works well unless you’re cooking at altitude, then an overnight soak is the best and easiest way. Unless you own a pressure cooker.

Some beans you can get away with not soaking at all, just cook them low and slow for a couple hours. I’ve done that with great northern beans.