A group of engineering proffesors got in a plane... Before closing the doors, the flight attendants told them that the plane had been built by their own students. Scared, all of the teachers ran out of the plane, except one. The pilot came to him and asked him why he was so relaxed. The proffesor said "I know my students very well. And I'm sure that if this plane is really built by them, the thing won't even start!"