Just after 2 p.m. Wednesday, a person in Corpus Christi, Tex., had just completed a transaction at a Bank of America A.T.M. when a surprise slid through the receipt slot.

“Please help,” read a handwritten note on a thin strip of paper. “I’m stuck in here, and I don’t have my phone.”

The person, whose age and gender the authorities did not provide, did not know quite what to do. But it so happened that a Corpus Christi police officer was driving by, so the person went a step beyond what other A.T.M. users had been willing to do and flagged down the officer.

The officer, like previous bank patrons, initially thought the note was a joke — some sort of “Candid Camera”-type prank that no one wanted to fall for.