One of the funniest “inside jokes” of The Big Bang Theory is the song that Sheldon’s mom used to sing to him when he was sick. It’s featured in three episodes, as you can see here:
The song is, like most lullabies, very simple. I came up with the chords earlier today, while jamming with my ukulele. Here they are, for all my musically-inclined nerdy readers. Corrections are welcome.
[G] Soft kitty, [C] warm kitty,
[G] little ball of [D] fur;
[G] happy kitty, [C] sleepy kitty,
[G] purr, [D] purr, [G] purr.
Interesting trivia: they are almost the same chords as The Lion Sleeps Tonight, except for a minor difference in the last verse that shouldn’t prevent the most creative among you to fit one into the other.
Should you prefer so, you could play it as C F C G / C F C G C or by whichever transposition makes you happy.