Why do people sing "Figaro" when they're pretending to do opera?

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Why: On "Extreme Makeover: Home Edition," Ty just sang, "Fiiigaro, Fiiiigaro."

Answer: It's part of the aria "Largo al Factotum" (by the character Figaro) in the opera The Barber of Seville. Here, it comes at 3:24-3:37 -


Source: Yahoo! Answers

The More You Know: The opera is by Gioachino Rossini, the same guy that wrote the "William Tell Overture."