In this paper we address the issue of stability in numerical methods f
or partial differential equations (PDEs) through normal mode analysis
of a particular scheme. It is shown that when numerical methods appear
to be stable, there are subtleties one must be aware of before conclu
sions may be drawn. This is illustrated through the analysis of the on
e-way wave equation using the leap-frog scheme. A bifurcation from sta
bility to instability is illustrated along with numerical simulations
illustrating the growing modes.