Since near-vertical rays are common, only small velocity contrasts are required to generate strong internal reflections. Figure 24 was computed by Kjartansson and used in a quiz. Study this figure and answer the questions in the caption. This will turn a pulse into a doublet that might easily be mistaken for two rays. There is a simple way to make constant-offset sections in laterally variable media when the reflector is just a point.
Convolution causes the travel times to add.
Too bad this technique doesn't work for reflector models that are more complicated than a simple reflecting point.