It was a scene straight out of South Florida, circa Election 2000, only there were no hanging chads or butterfly ballots to obsess over.

With a hand recount of some 91,000 votes cast in a Democratic primary for a district attorney post in New York City just beginning on Monday, it did not take long for the first commotion to arise: a stray mark discovered on a ballot.

A crowd immediately gathered. Lawyers for the two leading candidates, Melinda Katz and Tiffany Cabán, surrounded the ballot, along with officials from the Board of Elections. A poll worker held the ballot aloft, as eyes peered in .

Was the mark an accidental stroke? Or deliberate? If the latter, the vote, which had been cast for Ms. Cabán — who is trailing Ms. Katz by only 16 votes — would be declared invalid.