This card depicts what is known as an interference pattern with two point sources, such as drops in a pool of water. The dark bands for each represent peaks and the light bands, troughs. Here we see two types of interference: constructive and destructive. The former is where either the peaks or troughs of individual ripples meet, causing the resulting ripple to double in size. The latter is where each ripple cancels the other out, and in this case would be where a dark band overlaps with a light band.
If we consider each person as a point source, we can consider each interaction to be an act of either constructive or destructive interference. If constructive, it would reinforce each other, and if destructive, it would diminish the other.
Watch a live demonstration of an interference pattern in water, to help visualize a famous physics experiment to demonstrate the dual nature of light as a particle and wave simultaneously.
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