Must be Box2d. It's the only decent 2d physics engine available for as3, unless they used Haxe to built the swf and and accompany physics engine (http://haxe.or

Must be Box2d. It's the only decent 2d physics engine available for as3, unless they used Haxe to built the swf and and accompany physics engine (http://haxe.org/com/libs/physaxe http://haxe.org/com/libs/physaxe).