Comment by Stratoscope

I tried to look this up but wasn't successful. I remember it has to do with the lower pitch reed starting to vibrate along with the higher pitch reed, pulling the two notes together. But I don't quite understand the physics behind it.

If anyone find this, I am all ears! (Figurately and literally.)

While searching, I did run across this wonderful video of Toots Thielemans and Elis Regina:

https://www.youtube.com/watch?v=909HG10GLhE

And completely off topic, that somehow reminded me of my favorite live version of Ride Like the Wind:

https://www.youtube.com/watch?v=iYofDL0QnBE

No harmonica there, but everyone was having so much fun together!