Why does eating a mint make my breath feel cold?

You normally sense cold using a protein called TRP-M8 in the membrane of certain specialised nerve cells, which changes shape at low temperatures. This alters the ion permeability of the membrane, which triggers an electrical impulse. The menthol chemical in mint just happens to have the right molecular shape to bind to the TRP-M8 protein and distort it in the same way, even at normal body temperature.