Heterogeneous nucleation of D2 bubbles at the surface of the cathode is suggested as the cause of difficulties encountered in the reproduction of electrolytic coldfusion experiments. In some experiments, active nucleation centers are present only intermittently leading to a temporary increase in the chemical potential of deuterium in the cathode up to the homogeneous nucleation limit, which is ∼1.2 eV higher. The increased effective mass of electrons, expressed in the electronic specific heat and in the De Haas Van Alphen effect, is considered as a possible cause of cold nuclear fusion, along with the stronger heavy fermion effects directly observed at low temperatures, but localizability of these states remains a problem. Breakdown of the charge invariance of internucleonicforces at very low center-of-mass energies of the order of 1 eV applicable to this form of (non-µ-mesonic) coldfusion, leads to preferential tunneling of neutrons into nearby deuterons, which is suggested as an explanation for the conspicuous absence of neutrons and 3He.