A coin-flipping analogy and free corresponding web app have been developed to facilitate student understanding of the origins of spin-spin splitting. First-order splitting patterns can easily be derived and understood. "Complex" splitting patterns (e.g., doublet of quartets), are easily incorporated into the analogy. A study of the efficacy of the analogy/web app vs traditional lecture showed that the analogy worked as well as traditional lecture for overall NMR analysis, and better than traditional lecture for understanding the origins of splitting and why a signal has a given shape and peak-height ratio. The web app is freely available online, as discussed in the report.