We've heard of snakes on a plane, but what about sneaking on a plane?
They're calling her the "Serial Stowaway."
A 66-year-old woman from Illinois snuck on to a flight out of Chicago O'Hare International Airport last week ... and then made it all the way across the ocean to London.
Chicago police say Marilyn Hartman has a history of these sorts of incidents, and has been caught more than once in the past.
Somehow, she was able to get past security at O'Hare and then into the international terminal, where she boarded a British Airways flight to London.
So, how'd she do it? She hid inside the bathroom, of course.
After the airplane was in the sky, she came out and found a seat that wasn't already taken.
She would've gotten away with it all, but she attempted to get a passport once she landed in London.
She was denied and then taken into custody and returned to the United States.
Last year, she pleaded guilty to a trespassing charge and was sentenced to six months at a mental health facility, after she was found at a bus terminal at O’Hare.
She was also ordered to stay away from all airports, but apparently didn't listen.