Stumpers' idea of "zero-crossing FM detection" has been extended to analyze the phenomenon of FM threshold. The physical insight into FM threshold. In the subthreshold region, the position and number of zero-crossings is used to derive various formulas for calculation of noise power due to clicks in the presence of narrow-band Gaussian noise forthrightly. A two-state Markov model of the zero-crossing model for "clicks" is given. Thus, this is an alternative approach to Rice's "clicks" analysis and offers better physical insight into FM threshold. In the subthreshold region, the experimentally determined curves are better approximated by the zero-crossing model than by Rice's model.