Can you help me solve a puzzle? I remember the recent conversation about canons/rounds/two different songs sung at the same time. Is there a word for fitting lyrics from one song to the tune of another, and having an (almost) perfect fit?

The other day I heard someone do a haunting version of "O Little Town of Bethlehem" with her lovely voice and guitar. The words, were, of course, clearly familiar. The tune, vaguely so. Then it came to me... "The House of the Rising Sun". Try it! It works. But WHY??

Dani