This may not be very good, since it is my first problem - but here it goes...
There is a two-dimensional box and a point.
The point starts somewhere in the box and moves straight in some direction. When it hits a wall, it bounces off of it.
The point leaves behind a black line as it travels.
Is there ever a case where the entire box becomes colored if the point travels forever? If not, what is the minimum area of the "white space"?