Many years ago when I flew to China, the Beijing air traffic controller enquired about why was the 'door' wide-open on the left side of my fuselage, while my DC-10 was taxiing out for departure. I asked him which door? He said the small square door about half-meter by half meter on the port side of my fuselage. I think he was referring to the pressurisation dump valve, so I told him this is normal for DC-10, and the door will be automatically closed during the t/o run.
It seems they have never seen a DC-10 before.