A simple thermodynamic analysis evidences that ultrafine iron and nickel particles, assisting many carbon creating catalytic reactions, should fluidize in the course of such reactions, even if the reactions occur at sufficiently low or moderate temperatures. The main driving force of this fluidization is a sufficient oversaturation of the metal particles with carbon thus resulting in formation of metastable carbides with extremely low melting temperatures. The possibility of this fluidization allows explanation of some well-known phenomena of catalytic chemistry of carbon, like, e.g., rapid diffusion of carbon atoms through catalytically active metal particles, a tendency to unification of the sizes of the catalytically active metal particles in the course of catalytic processes, as well as formation of filamentous carbon of the "fish bones" structure.