Calcium oscillations present one of the most important signaling mechanisms in cell biology. The standard paradigm for the origin of calcium oscillations is dynamic, i.e. fast release of calcium from intracellular stores is followed by slow inhibition. Yet, this very dynamic theory for these oscillations came recently into scrutiny since the building blocks of cellular calcium signals are spatially and temporally limited calcium release events through small, distinct cluster of ion channels. According to this new paradigm, a coherent wave of calcium release, triggered by stochastic release events from a group of clusters, sweeps the cell. Oscillations are believed to emerge through a spatial coherence resonance mechanism. In this paper we investigate the difference in stochastic spiking generated by a small periodic system and a small excitable system and compare with published experimental data.