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The title refers to the return to Sheldon's life of his childhood hero Professor Proton who hosted a children's science show. From now on any episode with the word "Proton" in the title has a guest appearance from Bob Newhart.
This was Bob Newhart's first appearance in what became a recurring role as Professor Proton. Series creator Chuck Lorre had wanted Newhart to appear in one of his shows for years, and finally suggested The Big Bang Theory to him. Newhart agreed, as long as it was a recurring role, and the episodes would be taped live.
When Leonard and Sheldon try to comfort Professor Proton by saying that he inspired many children to take up science and that they "stood on his shoulders", it is a reference to a famous remark that Sir Isaac Newton made in which he said that, if he had seen further than others, it was because he stood on the shoulders of giants.
The title refers to the return to Sheldon's life of his childhood hero Professor Proton who hosted a children's science show. From now on any episode with the word "Proton" in the title has a guest appearance from Bob Newhart.
This is Bob Newhart's first appearance on The Big Bang Theory, which stars Simon Helberg, Previously, Helberg's father, Sandy Helberg, made multiple appearances on Newhart's show Newhart (1982).
"Soft Kitty" is sung when Sheldon sings it in the hospital to Professor Proton.