Hey, why’s the plane shaking?! Relax, it’s just an air pocket! You’re lucky — there’s a pilot next to you, flying as a passenger. They know much more about flights than you do, so a bit of turbulence won’t make them move a muscle. But if they start worrying about ice on the windows or sniffing the air for some reason, well, that’s when you should pay attention!
The thing is that no doors can prevent odors from traveling around. Some smells, such as super heated bleed air, fuel, or hydraulic fluid, are easily recognizable for a professional. And pilots know all too well that such scents can hint that there are some problems with the fuel-storage systems or the engine.