Way back in Season 1 of The Big Bang Theory, Sheldon (Jim Parsons) introduced the world to "Soft Kitty," a song his mother used to sing to him when he was sick. Over the years it's become one of the show's signature running jokes. Whenever Sheldon needs to be comforted, someone will try to cheer him up with "Soft Kitty."

On Thursday's episode of Big Bang Theory prequel Young Sheldon, we saw why exactly "Soft Kitty" is so meaningful to Sheldon thanks to a sweet scene between Sheldon (Iain Armitage) and his mother Mary (Zoe Perry). Sheldon had the flu, and Mary put a compress on his forehead and sang "Soft Kitty" to him until he fell asleep. It's a tender moment on a show that's come to be full of them.

Watch the clip above.

Young Sheldon airs Thursdays at 8:30/7:30c on CBS.

Iain Armitage and Zoe Perry, <em>Young Sheldon</em>Iain Armitage and Zoe Perry, Young Sheldon

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