I remember a flight I took on a 737 back in 1991. I was sitting a couple rows behind the wing in the window seat when I saw streaks of green fluid coming from the right engine. Hydraulic fluid is normally red. I think turbine oil is green. I notified a flight attendant who in turn notified the cockpit. The copilot came and spent several minutes examining the leak. We landed safely, but that example just goes to show that you can't completely isolate the cockpit from the rest of the plane. In an emergency, the cockpit crew sometimes has to be able to get access to different parts of the plane to examine the situation.