The "leans" occurs when a slight change in bank angle goes unnoticed by the pilot, resulting in a perceived angle of bank when the aircraft is rolled back to wings level. This is because*1 pointSufficient visual cues are not presentThe original bank angle goes is small enough that it goes undetected by the semicircular canals in the inner earThe pilot cannot "feel" the angle of bankThere isn't a suitable horizon

The "leans" occur when a slight change in bank angle goes unnoticed by the pilot, resulting in a perceived angle of bank when the aircraft is rolled back to wings level. This is because the original bank angle is small enough that it goes undetected by the semicircular canals in the inner ear.

The semicircular canals in the inner ear are responsible for detecting changes in rotational movement. When the bank angle is small, these canals may not register the change, leading the pilot to believe the aircraft is still in a banked position even when it has been rolled back to wings level. This can cause a disorienting sensation known as the "leans."

In addition, the lack of sufficient visual cues or a suitable horizon can exacerbate this issue. Without these visual references, the pilot may rely more heavily on their inner ear for orientation, which, as mentioned, may not accurately register small changes in bank angle.

Lastly, the statement that the pilot cannot "feel" the angle of bank is also true. The sense of balance and orientation in humans is primarily determined by the inner ear, not by physical sensation. Therefore, without visual cues or accurate information from the inner ear, the pilot may not be able to correctly perceive the aircraft's bank angle.