http://cs.sonoma.edu/~rpirie/pages/yodel.html A page with a lot of yodeling stuff.
If any of you have heard Grandpa Jones do T For Texas you would notice near the end of the song there is a break in his yodel, then a laugh, after which he finishes the song. Seems that was being recorded at the end of a long session, and his voice was just about gone. They quit and finished the recording the next day. Monument decided to leave in the laugh, and of course, that final yodel was done the next day.