Swedish air operator SAS on Tuesday cancelled a flight from Stockholm to Chicago because of an unruly passenger, a mouse.
The rodent was spotted ahead of boarding on the 0815 GMT flight but evaded the many mousetraps laid to catch it, SAS said.
Company spokesman Anders Lindstroem said: "For safety reasons, you don't board when there's a mouse on board.
"We hope to find it overnight," he said, adding that the 250 passengers on the Airbus A330 flight had been understanding.
Apart from disturbing passengers, a mouse on board a flight is a potential danger as it could creep in amongst cables, Lindstroem said, adding that a complete inspection would be carried out once the mouse was caught.
The spokesman said it was the first time a mouse had been discovered on an SAS plane.