An Ivy League European professor was offloaded from a flight in the United States, after his co-passenger thought a math equation he was working on was a sign he was a terrorist, PTI reported. Guido Menzio, a professor at the University of Pennsylvania, said he was taken off the flight and questioned for two hours after a woman alerted cabin crew about him. He was reportedly solving a differential equation he was working on ahead of a speech he had to give at Queen’s University in Ontario.

American Airlines confirmed that a woman passenger had expressed concerns about Menzio on the flight. Menzio said the woman claimed she was unwell, after which she passed a note to a flight attendant. She said that she was too ill to take the Air Wisconsin operated flight. The flight, from Philadelphia to Syracuse, was delayed by more than two hours as a result.

Menzio had told The Washington Post he was treated with respect when asked to disembark, but questioned a system that relied “on the input of people who may be completely clueless.” “Not seeking additional information after reports of ‘suspicious activity’ ... is going to create a lot of problems, especially as xenophobic attitudes may be emerging,” he said.