An economics lecturer's flight was delayed after a fellow passenger mistook a maths equation he had written as terrorist writing, he claims.
Ivy League professor Guido Menzio, of the University of Pennsylvania, said the passenger mistakenly thought the equation was a sign he was a terrorist.
American Airlines confirmed that the female passenger had expressed suspicions.
Professor Menzio was flying from Philadelphia to Syracuse on Thursday and was solving a differential equation related to a speech he was set to give at Queen's University in Ontario, Canada.
But the woman sitting next to him passed a note to a flight attendant and the plane headed back to the gate.
Professor Menzio, who is Italian and has curly, dark hair, said the pilot then asked for a word and he was questioned by an official.
"I thought they were trying to get clues about her illness," he said.
"Instead, they tell me that the woman was concerned that I was a terrorist because I was writing strange things on a pad of paper".
Professor Menzio explained what he had been doing and the flight took off soon afterwards.
The female passenger, who claimed she was too ill to travel, was rebooked on a later flight.