It's more likely that the mouth opening is a natural, unconscious reflex that happens for several reasons:
* Concentration: Applying mascara requires a delicate touch and precision. Opening the mouth slightly can help some people focus and steady their hand.
* Facial tension: Holding your breath or tensing up your face while applying makeup can lead to a slight opening of the mouth.
* Muscle coordination: Applying mascara involves using small, precise movements, and the mouth may open slightly as a part of the body's natural coordination.
It's important to avoid generalizations and stereotypes. People, regardless of gender, apply makeup in different ways, and there's no single reason why someone might open their mouth while doing so.