Keen observers may have noticed a familiar face briefly popping up in the background of last night's episode of "How I Met Your Mother." Conan O'Brien had an incredibly brief cameo on the show. His role was so brief he was, for all intensive purposes, playing an extra on the popular CBS sitcom.

O'Brien didn't speak, didn't address other characters, and he was on screen for approximately three seconds. He is merely having a beer at the "How I Met Your Mother" gang's main hang out, McLaren's pub.

His extremely small role raises questions: Was that really him gracing the sitcom's background? Why would a comedic legend like O'Brien accept such a small role?

But, your eyes did not trick you that was the real Conan O'Brien, not some Conan O'Brien look-a-like trying to break into acting. And rest assured O'Brien did not accept the tiny role because his career is taking a huge nosedive and it's all he could get. The real story is simply that Conan O'Brien thought it would be funny.

 In June, Neil Patrick Harris appeared on "The Conan O'Brien" show and the two discussed a playwright benefit they had attended together. After the benefit's performances there was a live charity auction, and one of the prizes was a walk on role on "How I Met Your Mother."

Harris said the show often offers that prize at charity auctions. According to Harris, O'Brein said that was the only item he would bid on, and he then went on to outbid himself until he felt he had donated enough money. Thus winning a walk on role the hit CBS show.

O'Brien said the producers of "How I Met Your Mother" were going to write him in as a character, but he told them not to because he thinks "it's much funnier if I'm in the bar in the background. " And Neil Patrick Harris agreed.