Whether or not The Big Bang Theory comes to an end after its next season, few would argue that the egghead comedy kept alive many a three-camera sitcom tradition, aided by memorable moments the likes of Sheldon’s “Soft Kitty” lullaby. The memorably kitty-ditty has been featured no less than seven times over nine seasons, but has now come under fire with a lawsuit over its inception.

The Associated Press reports that late poet Edith Newlin’s daughters Margaret Perry and Ellen Chase have filed suit that The Big Bang Theory has infringed on copyrighted work belonging to their mother, who herself died in 2004. The suit claims that “Warm Kitty” (and thereby its TBBT derivative) was written in 1937, the CBS series swapping only “Warm” and “Soft” in the lyrics.

Warner Bros. itself declined comment, though Willis Music offered an explanation to Deadline of the apparent rights discrepancy:

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.

Perry and Chase have both alleged that their mother’s lyrics have become integral to the show, both in character development, overall success and merchandising, but it remains to be seen if the suit will hold up in court.

Depending how much life The Big Bang Theory retains regardless, might we have seen the last of “Soft Kitty”?

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