SAN FRANCISCO—A little mouse bypassed security check and got on board a British Airways flight causing a four-hour plane delay on Wednesday, March 1. Passengers were traveling from London to San Francisco.

While the rodent appears harmless, the mouse could have caused engine failure by chewing of wire and potential health problems. It is still unclear on how the rodent was able to board the plane, but regulations stated that the plane is not authorized to take off.

Passengers from the Boeing 777 had to be send back to the airport and wait for a new plane to become available.

“Somebody saw a mouse that scurried under one of the doors,” said passenger Chris Claeboe to ABC 7 News. “They kept us on the plane for about 15 minutes. Told us we had to get off the plane because we couldn’t fly with a mouse.”

Passengers were able to board a new aircraft. Members of the crew made jokes about the incident to keep the passengers with a positive attitude.