Two other notable things about this game: lives and physics. You begin each level with as many lives as there are balls in the arena, and the only thing you can ever sacrifice is a life. The idea behind the lives is that any time you try to build a wall, you are putting one or two of your lives on the line (one in each direction from where your mouse pointer appears in the arena). The walls, as you build them, are built at a fixed speed; if any ball hits one of your walls while you build it, your wall dies and you lose a life. As you approach higher and higher levels (e.g. 20+), it becomes effectively impossible to win without losing lives, because of the physics of the game.
The arena is a fixed size. The balls bounce at one of two set speeds (fast or slow). As the number of balls increases (each successive level adds one more ball to the arena, except 49->50 [see w/u by Enzondio above]), the pressure increases as well, so building a wall that crosses the entire arena becomes essentially impossible as the levels increase above 10. The physics model is similar to that of atoms in a fixedly-sized container, where having more atoms in the same space (and the atoms travel at a fixed pace) increases the pressure. Below I show the space where the game is played on level 6: "|" and "_" are the playing field, "X" is the background, a diamond is a ball; the lower right-hand corner is altered because it's supposed to look like a wall was built there as a trap, and one ball is already trapped there.
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