Overreaction of the wave in fingerwaving may be caused by:

In finger waving, overreaction of the wave refers to an exaggerated or overly defined curvature in the hair that deviates from the intended soft waves. When pinching or pushing the ridge during the waving process, it can disrupt the natural flow and structure of the wave. This manipulation can create sharp angles or overly tight creases instead of smooth, flowing waves, leading to an incorrect appearance that is not aesthetically pleasing.

Using too much product would typically cause the hair to become weighed down or greasy, which could affect the overall look but wouldn't directly cause overreaction in the wave pattern itself. Improper tool usage might lead to uneven waves or difficulty in setting the hair, but this issue relates more to technique than to the specific problem of overreaction in terms of wave definition. Inconsistent temperature can affect the setting process of the hair, but it doesn't specifically cause the wave to overreact in the way that manipulating the ridges does.

Thus, pinching or pushing the ridge is a direct action that can lead to the unwanted outcome of exaggerated wave reactions, making it the most relevant cause among the options provided.