A United flight from Chicago to Jacksonville was delayed Monday night because of a pet ferret, according to passengers.

Passengers told First Coast News the woman got on board claiming that the ferret was her service animal. However, the woman did not have the documents to prove it.

In the end, the woman was allowed to board with her ferret and the plane arrived in Jacksonville.

According to passengers, the flight attendants said the airline employees should have checked documentation before letting the ferret on board.

United said it is now investigating the incident.