https://www.yahoo.com/news/m/812c4963-b823-3207-b25a-ddd9c71649b8/%26%2339%3Bbig-bang-theory%26%2339%3B.html

The “Big Bang Theory” had a big legal victory on Tuesday. A Southern District of New York judge granted a motion to dismiss a lawsuit against Warner Bros. and Chuck Lorre Productions that claimed the lyrics of the show's often-sung “Soft Kitty” rhyme infringed on a copyright. Warner Bros. and Chuck Lorre Productions were initially sued back in 2015 over the rhyme sung to Jim Parsons’ Sheldon character. The suit was brought on by Ellen Newlin Chase and Margaret Chase Perry, the daughters of Edith Newlin, a former nursery school teacher, who died in 2004. Newlin’s daughters claimed the song featured on “The Big Bang Theory” used the lyrics their mother wrote and published in the 1937 compilation

I would think something like a nursery rhyme would belong to the public domain anyway. This is the first I've heard that something like that could be copyrighted.