Perception of the Amount of Fluid in a Vessel Shaken by a Hand
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As fluids are an important part of natural environment, it can be expected that humans, as well as other animals, have the ability of picking up information about their properties. One aspect of fluids which makes them decisively different from solid objects, is their relation to vessels. They have no form of their own, but "borrow" it from the vessel that contains them. Their form also easily changes when the vessel is moving. (cf. what may happen when you move a glass with liquid.)

There are indications that we may be able to use information provided by the changing form of a fluid in motion for perception of more permanent properties of it. One everyday example is when we shake a nontransparent vessel, such as a milk carton, in order to be informed about how much of its original content is left. In this situation, there is, hypothetically, information available from the dynamic changes of the fluid to be picked up by haptics, sounds to be picked up by hearing, and movements of the shaking hand to be picked up by sight.