The Big Bang Theory has introduced a number of iconic catchphrases and sayings into the pop lexicon. But none perhaps as beloved as the lyrics to 'Soft Kitty'. The lullaby is often sung by Sheldon Cooper when he needs comforting. But a new lawsuit may have him paying big royalties the next time he coerces one of his friends to accompany him in performing the catchy ditty.

The song has been sung several times over the course of the hit series' 9 season run. The song became so popular, CBS built a marketing campaign around it. And there have been plenty of merchandise for Soft Kitty, including plush toys, T-shirts and coffee mugs. Poet Edith Newlin wrote the lyrics for 'Warm Kitty' in 1937. And now her daughters Margaret Perry and Ellen Chase believe they are owed compensation. And they're demanding that CBS pay up. In they suit, which was filed in Manhattan today, the pair had this to say.

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"The Soft Kitty lyrics have played a prominent role in the development and portrayal of one of the central characters in the program."

The Soft Kitty song was first introduced in Season 1, in the eleventh episode titled The Pancake Batter Anomaly. It has subsequently been sung on 7 more episodes. At this time, Warner Bros., who produces the show, has declined to comment.

Willis Music purchased the book the song appeared in nearly 80 years ago. They claim that they properly and legally licensed the song to Warner Bros, for the TV series. Performance rights organization ASCAP lists Warner-Olive Music (a subsidiary of the Warner Music Group) as the song's publisher. This suggests that the rights were transferred from Willis Music. Willis Music owner Kevin Cranley had this to say on his company's website.

"In 1937, we published a book called 'Songs for the Nursery School,' and we sold tens of thousands of copies. It is a hardbound book of over 150 songs for children. The book was written by Laura Pendleton MacCarteney. In that book on page 27 is Warm Kitty. Warner Brothers and I worked together to secure the rights for the show The Big Bang Theory and they have been using the song ever since. The writers wanted the song because one of them remembered it as a child. They also wanted to slightly change the words and I'm really not sure of the reason for that change."

The original lyrics written by Poet Edith Newlin, adapted from an English folk tune, are as such.

"Warm kitty, soft kitty, little ball of fur; Happy kitty, sleepy kitty, purr! purr! purr!"

Hardcore fans of The Big Bang Theory know that some of the lyrics have been swapped around. The key legal issue in this case, which will see it move forward, is whether or not the publisher acquired the rights to the songs contained in the book when they secured the rights to MacCarteney's book. If they did not, Newlin's daughters may have a legal leg to stand on. But if the publishing company did acquire the song rights when obtaining the book, the two woman stand to lose. Especially since most publishing agreements have the songwriter assign their copyrights of the lyrics to the publisher. The case will essentially come down to the wording of the contract. The suit goes onto state the following.

"The Soft Kitty Lyrics are among the best-known and most popular aspects of The Big Bang Theory. They have become a signature and emblematic feature of the show and a central part of the show's promotion."

The question is whether or not Newlin assigned the copyright of her song to the book publisher when she gave MacCarteney the right to publish her song in the book. If she did, then MacCarteney would have had the right to transfer the copyright to Warner Bros. for use in the show. If not, the poet's heirs maybe entitled to any profits from the use of said song, including merchandising dollars.