What's the difference between a hole and a void? A hole implies that something was there to begin with, whereas a void has always been completely empty.
Presumably it would refer to ey hole itself, which is the opening in your mouth. It could then refer to either your lips or perhpas to food, as both certainly filled the hole (or covered it up in the cas of lips) at one point or another.
I always thought of "void" to be an empty place that cannot be filled, that you can get lost in it, if big enough, that nothing exists inside of it. A hole can be a tunnel or a formation that resembles a bucket.
