The heirs to a poet who claim their mother wrote a poem popularized in the TV series The Big Bang Theory are suing CBS and others connected to the sitcom for allegedly using the "soft kitty" lyrics without their permission on at least eight episodes.

The lawsuit, filed last Wednesday in a New York federal court, claims that the lyrics beginning with "Soft kitty, warm kitty" were created by Edith Newlin some eight decades ago and published in 1937 in a book called Songs for the Nursery School. The suit says the book's copyright registration was renewed in 1964, which "served also to register and renew" Newlin's copyright.

"Defendants have used the Soft Kitty Lyrics without authorization in their entirety as an emblematic feature of The Big Bang Theory, contributing materially to the program's enormous success, and in promotion and advertising for the show," according to the suit (PDF). "Defendants have also used the Soft Kitty Lyrics in their entirety on a wide range of merchandise items, from t-shirts to air fresheners, as part of one of the largest global licensing and merchandising programs ever mounted for a live-action television series."

The suit claims that Kentucky-based Willis Music, which copyrighted the book where the lyrics first appeared, erroneously granted Warner Brothers the rights to the lyrics in 2007 so they could be used in the show.

"Defendants not only willfully infringed Plaintiffs' copyright, but they failed to credit Edith Newlin as the author of the Soft Kitty Lyrics. Instead, they placed a credit line on some merchandise items that made it appear as if one of the Defendants themselves created the soft Kitty lyrics," the suit claims. "The credit states that the Soft Kitty Lyrics were 'Written by Bill Prady.' Bill Prady is a principal of Defendant Chuck Lorre Productions, one of the producers of The Big Bang Theory."

CBS did not immediately respond to a request for comment.

Newlin, a former nursery school teacher in New Hampshire, died in 2004, according to the suit. Newlin's heirs claim that the lyrics in question have "played a prominent role in the development and portrayal of one of the central characters in the program, Sheldon Cooper (played by Jim Parsons), who is presented as a brilliant scientist with the emotional maturity of a child. As Sheldon has let others know in the course of the sitcom, beginning in the show's first season, his mother sang the Soft Kitty Lyrics to him as a child, and he still wants them to be sung to him when he is sick. Sheldon in turn sings the Soft Kitty Lyrics to other characters on the show who are sick or troubled."

The suit, which seeks unspecified damages, says that characters or producers from the show led audiences at Comic-Con conventions in singing the lyrics. One of Newlin's daughters learned of the alleged infringement in 2014 while researching her mother's history, according to the suit.

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