the song his grandmother sang
in case anyone else tries to find it, i'll save you the time it took me
https://www.youtube.com/watch?v=rFl_ZetKiNA
For those who were curious but didn't click on the above link, the title of the song River hummed is "Kristallen den Fina".
Here's another version by The Real Group, fully a cappella.
http://youtu.be/6VhZx_7wEzs
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