Repetitive spontaneous calling in frogs and electric signalling in pulse-type electric fishes are driven by neural pacemakers. Minimization of signal overlap between neighbors is achieved in frogs and certain electric fishes by mutual entrainment, requiring cycle-by-cycle adjustment of pacemaker interval. Other fishes, which require a regular electric organ discharge, are more constrained in their ability to avoid jamming. Entrainment may also serve to reciprocally place signals in a temporal ''blindspot'' of the receiver, the period of elevated sensory threshold following signal production, to reduce aggressive interactions.