“Warm Kitty” is a children's song, popularized by the characters Sheldon and Penny in the American sitcom The Big Bang Theory where it is rendered as “Soft Kitty”. The words to “Warm Kitty” were written by Edith Newlin, and are still under copyright. The tune was taken from a traditional English children's song, “Little bird, have you heard…” but the note values had to be changed to fit the new words.[original research?]
In the The Big Bang Theory, the lyrics are “Soft Kitty, Warm Kitty, little ball of fur. Happy Kitty, Sleepy Kitty, purr, purr, purr”. This is sung by Sheldon, Penny, and Sheldon's mother. They sing it to each other when one of them is sick or can't sleep.[original research?]
Versions of the song have been released by Australian children's performer Patsy Biscoe, and by the long-running ABC children's programme Play School. However, their rendition has the lyrics: "Warm Kitty, Soft Kitty, little ball of fur. Sleepy Kitty, Happy Kitty, purr, purr, purr".[original research?]
By Christmas 2011, “Soft Kitty” merchandise such as a plush stuffed singing cat or T-shirt with The Big Bang Theory version of the lyrics could be purchased.