‘The Big Bang Theory’ and network CBS are being sued by the heirs to a New Hampshire teacher over the ‘soft kitty’ song featured in the show. The daughters of Edith Newlin, who wrote a poem about a "soft kitty” in the 1930s, claim the show is violating their copyrights by using the lyrics.

Big Bang Theory‘The Big Bang Theory’ is facing legal issues over its ‘Soft Kitty’ song.

Fox News reports that the lawsuit claims the show used lyrics written by Newlin without buying the rights. It claims that in 2007, Warner Bros. Entertainment and the show's other producers sought permission to use the poem’s lyrics from Willis Music Co., a Kentucky-based company that had published them in a book called Songs for the Nursery School.

But while Willis Music gave permission to use the lyrics, the suit claims they did so without consulting Mrs Newlin's heirs, even though the book makes clear that Mrs Newlin was the author of and owned the copyright to the lyrics.

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The lawsuit states that the ‘Soft Kitty’ lyrics have been used in their entirety on at least eight episodes of the show since March 2008. It also adds that the lyrics have also been used in merchandising, including being displayed in their entirely on T-shirts, sweatshirts, hoodies, pajamas, mouse pads, mobile phone covers, wallets, air fresheners, refrigerator magnets, singing plush toys and other products.

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

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According to the lawsuit, Ellen Newlin Chase, Ms Newlin’s daughter, learned of the show's use of her mother’s lyrics in August 2014, when she was researching her mother's history for an article and came across a blog post discussing the use of the lyrics in the show.

The suit also claims that the defendants not only have failed to credit Newlin but have on occasion made it seems as if the lyrics were written by one of the show's producers. Neither CBS nor any of the parties involved have so far commented on the suit.