Anything that has the property to flow is considered as fluid . So thoughts have an ability to flow inside our mind hence it comes under the category of fluid. Since the liquid and gases assume the shape in which they go , our mental thoughts also have the capability to assume the shape of any object.
Mental Particles are the Hypothetical smallest coded particles present inside mind which are related to the materialistic world. These coded particles temporarily acts as a reference to every quality and quantity of the materialistic world. When some one finds a similar quality or quantity our brain gets excited to change or add the information to our existing knowledge.