What is the name of the lullaby Sheldon sings when sick?

The name of the lullaby Sheldon sings when sick is “Soft Kitty.” In The Big Bang Theory, Sheldon repeatedly turns to the song for comfort when he has a cold or feels unwell, often asking someone nearby to sing it to him.

The song’s lyrics describe a soft, warm, sleepy kitten and end with the familiar “purr purr purr.” The show presents it as a song Sheldon’s mother, Mary Cooper, sang to him during childhood. Penny, Leonard, Amy and other characters also sing it to him over the course of the series.

“Soft Kitty” was popularized by the sitcom but is based on older musical traditions. Its melody traces back to the Polish children’s song “Wlazł kotek na płotek,” while an English version called “Warm Kitty” appeared in an American children’s songbook. That variation explains why some viewers remember the title as “Warm Kitty,” but the canonical title used in the show is “Soft Kitty.”