(CNN) -- There's a small, mysterious group of people in the United States who are almost indistinguishable from their neighbors. But they're different in an important way and they could decide today's presidential election.
After a campaign that has dragged on for two years, cost more than $2 billion, attracted record turnout in the U.S. and generated strong opinions worldwide, there are actually some voters who haven't made up their minds.
Among decided voters, Barack Obama has a commanding lead. But it's not an insurmountable one and John McCain could still win if he can nudge the numbers in his direction.
The undecided appear in most polls as four to nine percent of the sample. In several U.S. states that's enough to change the outcome.
Humorist David Sedaris says "I think of being on an airplane. The flight attendant comes down the aisle with her food cart... Can I interest you in the chicken? she asks. Or would you prefer the platter of (filth) with bits of broken glass in it?
"To be undecided in this election is to pause for a moment and then ask how the chicken is cooked."
Pollsters believe that the undecided voters tend to be older women of modest education and income, who haven't paid much attention to the campaign.
If they are truly undecided, there is no easy way to predict what they'll do today. Without a firm preference, how many will actually bother to vote?
Millions of Americans already have voted. Advance balloting has set new records and turnout today is expected to set records in many areas as well.
The vast majority of voters have known for a while what they plan to do. They weren't about to be convinced otherwise. So, in the last few days the campaigns have done their best to win over the last holdouts - the voters who hadn't decided.
Not quite as informed, not quite as enthusiastic, but we'll see very soon whether they offer the surprise ending to an election that seems nearly sewn-up.