The lack of reproducibility of the cold fusion experiments, aggravated by the great diversity and inconsistency of the positive results, implies that these nuclear phenomena are hypersensitive, i.e., correlated to a “chaotic” factor. All the factors considered so far, such as structure, transformations, or defects of the crystal lattice; bubbles of deuterium; dendrites, etc., are insufficiently chaotic to explain the known facts. Experimental data suggest that nuclear reactions take place in active sites on the surface of the lattice, that they are stimulated by dynamics factors, and that they represent an extreme form of heterogeneous catalysis. Consequently, according to modern ideas concerning catalysis, the desired chaotic factor is the surface dynamics of some metallic deutendes (hydrides). This hypothesis, called the surfdyn concept, is compatible with all published data, explains the peculiarities of cold fusion, and must be supported by an adequate theory describing the nature and mechanisms of the different nuclear processes.