40-year-old University of Pennsylvania economics professor Guido Menzio was traveling from Philadelphia to Syracuse on Thursday.

He was solving a differential equation, when suddenly, as he describes it on his Facebook page, "The passenger sitting next to me calls the stewardess, passes her a note."

The plane then came back to the gate, and the passenger left, while Menzio was requested to leave the plane, too. He was then "met by some FBI looking man-in-black."

"They ask me about my neighbour. I tell them I noticed nothing strange. They tell me she thought I was a terrorist because I was writing strange things on a pad of paper. I laugh. I bring them back to the plane. I showed them my math," Menzio wrote.