click green flag and just watch or try out dragging one of the circles to see what moving one set of lines over the other looks like, especially when they are close to parallel but not quite the number in the corner is the direction of the rotating lines. when the number gets close to 90 or -90, look for the moiré effects ! :D
this is just two sets of parallel lines, where one rotates direction. the wobbly, wavy, or stripey effects you see when the rotating set is almost straight up-and-down are moiré patterns got inspired looking at the wikipedia page for moiré patterns :) moiré patterns are a category of interesting effects that happen when two similar, but slightly different patterns move are laid across one another
