many women do but it helps to keep their eyes from closing while using the brush on their eyelashes, usually people that have been using make-up for a long time don't because they're used to the brush on their eyes. hope i helped!
Not true at all. I put it on with my mouth closed.
Many women probably do that because of the angle they tilt their head at when they lean in towards the mirror. When you're in that position, it's more comfortable to just let your jaw hang loose.