The passenger might eat your face off. Happened to that poor boy on a coach up in Canada a few years back. I’m still horrified by that story.
That sounds awful. Once, a woman sat next to me on a plane with a small dog, she said it was her emotional support animal. But she asked me if I was allergic, I said no, and then she said if he bothered me let her know and she would put him in his carrier.
So her attitude and care for my feelings was OK so I was fine. If it had been a different dog and a different human I probably would have said I was allergic.