“Happy Birthday to You,” the most recognized song in English, is not actual public domain. It is still under copyright in the United States until 2030 and in Europe until 2016. Filmmakers and the likes have to pay royalties to use that song. Most of the time they just avoid the song or use “For He’s a Jolly Good Fellow” instead. I learned that while watching Disney Channel with my sister. LOL!
(Just posting a quickie to get back on track. I was two days behind on posts but not anymore.)