A US-bound plane was unable to take off from Heathrow Airport after a mouse was spotted on board.
Passengers on the 10:40 GMT British Airways flight to San Francisco were strapped in and waiting to leave when the "rather unusual occurrence" was announced.
The crew told passengers planes cannot take off with mice on board, and that another flight would be scheduled.
It eventually left about four hours later.
One passenger, Carly, said there was "general disbelief" among she and her fellow travellers when the news was broken.
"I'm not sure people knew how to react," she said.
She said they had been told another plane had been found, but the passengers would have to wait several hours for a gate to be found before it could take off.
Some of the flight's passengers tweeted their reactions.
Matt Watt
"Just had my flight to SFO cancelled because of a mouse on board the plane. Could it not get a visa?? #britishairways", while
a Haiku: "About to fly to SF, There is a mouse on the plane, We all must get off."
He also
"I'm going to sell this to the movies. It can be the slightly more pedestrian prequel to snakes on a plane. Maybe this is what lured them on?"