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The kinds of electrical-arc cathode spots described in literature are analyzed. Division of spots into two types qualitatively different in natureÂ¿explosive spots and thermal spotsÂ¿is proposed. The observed microsecond oscillations of the brightness of a rapidly moving spot are interpreted in terms of heat accumulation in the cathode and random motion of the spot. The transition of the spot to a thermal region is analyzed and the lifetime of nonstationary thermal spots is shown to be proportional to their size squared.