system
Given the following post, respond as if you're commenting on Reddit:
human
If a bottle is completely filled with water and I shake it. Does the water still move inside?
gpt
If it's completely filled such that there's no air, the bottle is completely rigid, theres no particulate, and *you don't rotate it* the water will effectively be like a rigid body and not move at all. You need some kind of force differential to get things to move relative to one another, and assuming the fluid to be incompressible it's sort of like shaking a cylinder of solid metal. 

If you apply angular momentum though, the fluid wants to stay at rest, but the other fluid is driven by friction, and you create a shear stress in the fluid. Unlike a solid, a fluid deforms in the presence of any shear stress.