At first, no one paid much attention to the group of five when they erupted into song in the middle of Clyde's restaurant in Georgetown.
But as the melody grew, diners began lifting their heads from their plates, poking one another and pointing - most with the same quizzical looks on their faces.
"We're not used to getting music in here," said Cherie Calvert of Kensington, "just martinis."
The colorful members of High Five, the night's impromptu entertainers, aren't used to being together without performing, either, regardless of where they are - they claim it's nearly impossible to refrain.
"You know that Dr. Seuss book Green Eggs and Ham?" asked Susan Dargusch, the group's second soprano. "Well, that's us: We'll sing in a box; we'll sing with a fox. We'll sing in a bar; we'll sing in a car."
But tonight, the a cappella jazz quintet actually has a planned (but still unpaid) gig. They're singing at the Howard County Central Library as part of its new monthly music program, Third Thursdays in the Cafe', and their aim is to wow you with nothing but their voices.
"You can equate us with stuff like the Manhattan Transfer without a backup band," said bass Mike Kelly, whose North Laurel house is the quintet's home base. "We're not a band; we're a group. We don't use instruments."
What they do use are their vocal cords and considerable musical training, which spans barbershop quartet to classical, to produce notes that often resemble instrument sounds.
"If you close your eyes, there are so many sounds it sounds like instruments," said Dargusch, 37. "That's the fun thing for us: to try and become trombones or clarinets."
"We're bigger as a group than we are as individuals," said High Five's founder, tenor Joe Mannherz, who has sung with the Baltimore Symphony for the past quarter-century.
Most of High Five's members don't expect to be able to quit their day jobs anytime soon. The year-and-a-half-old group did get a big nod from the a cappella community last month when they placed third as the best group overall at CASA's Mid-Atlantic Harmony Sweepstakes. But for the most part, they're keeping their dreams grounded in reality.
"We just like singing," Kelly said. "We could sing in a basement, and we'd be happy."
High Five performs tonight at the Howard County Central Library's cafe', 10375 Little Patuxent Parkway, Columbia, at 7 p.m. Admission is free. Information: 410-313-7800 or www.highfivelive.com.