Why can covering one receptor cause an animal using tropotaxis to move in circles?

In the context of tropotaxis, an animal orients itself by making simultaneous, automatic comparisons of stimulus intensities between paired receptors on opposite sides of its body. This mechanism allows the organism to maintain a direct path by balancing the input from both sides.1

When one receptor is effectively covered, the animal loses the ability to perform this bilateral comparison. Because the organism can no longer detect or balance the stimulus on that side, the automatic reflex to maintain symmetry is disrupted. Consequently, the animal continues to turn toward the side that is still receiving stimulation, resulting in a continuous, circular path known as a circus movement.1