Melody is not copyrighted. The words are. The melody is much older. From article:

>The melody for Happy Birthday was first penned by two sisters from Kentucky, Mildred J. Hill and Patty Smith Hill. The song was called Good Morning to All, but bore the recognizable melody. The tune was first published in 1893 in the book Song Stories for the Kindergarten. The melody has since passed into the public domain, and is safe to hum in public without permission.

No, the melody was originally called Good Morning to All and has been around since 1892, IIRC. The Warner/Chappell claim is based on the lyrics, which just barely meet the threshold requirements for something to be even identifiable as a work.

I truly don't know, but I imagine that if you were wearing birthday hats, consuming cake or some other celebratory baked good, and clearly not worshiping an Egyptian river god, there may be a problem or two convincing someone you weren't singing the copyrighted words.

Given that Robin Thicke got sued just for writing a song that kind of has a little bit of the same feel as a Marvin Gaye song, I doubt this works.

No, because it is obviously a derived work. It's extremely unlikely someone who never heard the tune "Happy Birthday" would come up with lyrics for the (non-copyrighted) melody that sound exactly like the copyrighted lyrics by sheer coincidence.

You could, however, use entirely different lyrics. But I'm pretty sure it could still be assumed to be a derived work as long as it's a birthday song.

Disclaimer: IANALATINLA, etc