Oscillations of free intracellular calcium concentration are thought to be important in the control of a wide variety of physiological phenomena, and there is long-standing interest in understanding these oscillations via the investigation of suitable mathematical models. Many of these models have the feature that different variables or terms in the model evolve on very different time-scales, which often results in the accompanying oscillations being temporally complex. This talk will discuss attempts to explain a particular type of complex oscillation seen in a model of calcium dynamics in hepatocytes (liver cells), and in particular will talk about challenges for the application of geometric singular perturbation theory and numerical bifurcation analysis in this context.