Comedy legend Bob Newhart brought his signature stammer and dry wit to "The Big Bang Theory" as one-time children's entertainer, Professor Proton. Both Leonard and Sheldon had grown up glued to his show, which they said was a big reason they got into science in the first place. So when they found out he was available for parties now, they quickly hired him.

Unfortunately, the good professor was under the impression that he was going to be doing his act for kids, as opposed to grown men who were already respected scientists. And nobody can be prepared enough for dealing with Sheldon.

When they met him -- in the stairwell, as they'd neglected to tell the 83-year old that the elevator didn't work -- Sheldon was as excited and creepy as expected. He leaned in real close at one point and said, "I can get as close to you as I want without my mom saying it’s going to ruin my eyes."

The professor understandably asked if Sheldon was dangerous. "He's a genius," Leonard responded, but that didn't answer the question.

In the end, trouble with his pacemaker sent the professor to the hospital, with Sheldon not far behind. At his bedside, Sheldon was asked to take over for Professor Proton's next party -- he could be Professor Proton, Jr.

Newart told The Hollywood Reporter that it took a while for him and "Bang" creator Chuck Lorre to work out the details of this gig, but one of his stipulations was that it be a recurring opportunity.

After proving he's as funny now as he's ever been, fans new and old will probably be more than happy to welcome Professor Proton back to the "Big Bang" universe any time. There are only two episodes left of "The Big Bang Theory" this season, Thursdays at 8 p.m. ET on CBS.

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