CBS being sued over The Big Bang Theory 'Soft Kitty' song

American television network CBS are being sued over their use of a nursery rhyme in the popular comedy series ‘The Big Bang Theory’.

A case filed by Ellen Newlin Chase and Margaret Chase Perry claims that the hit TV series has been using lyrics written by their late mother in a poem about a “soft kitty” without buying the rights to use the words.

The “Soft Kitty” lullaby has been sung by characters in ‘The Big Bang Theory’ on numerous occasions and is often performed by characters Penny, played by Kaley Cuoco, and Sheldon Copper, portrayed by Jim Parsons, when either one of them is feeling sick.

The lawsuit filed by claimants states that: "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 ‘Soft Kitty’ lyrics have been featured on merchandise promoting the show as well as featuring in the script.

Despite Warner Bros. Entertainment being granted the right to use the lyrics in question from Willis Music Co. - a Kentucky-based company that had published them in a book called ‘Songs for the Nursery School’ – the Newlin heirs claim they were not consulted about the arrangement despite the copyright belonging to their mother.

Listen to ‘Soft Kitty’ being sung below: