>>13711228Don't read this comment if you want to solve the problem my yourself.
The answer is the second-to-last letter in the word "letter." Both circles are walking to the right, and, when they reach the 4th column, they get back to the 1st column in the next row, like Pac-Man idk. Both move 1 square every new image.
However, the grid is being consumed by a chain pattern of white squares. Every this a white square falls directly over one of the circles, the circle changes color (from blue to white or from white to blue) and keeps walking.
