if you hold the mouse button down and drag it of the screen, let go, and drag the mouse onto the screen, it will let youre guy keep shooting without having to hold the mouse down
its a fun game but if you want an even beter portal download steam and the portal first slice download for free. the first slice contains the first 11 levels of the real portal.
 "Omega Box"){kind=icon}
 "The Line Game: Orange Edition"){kind=icon}
 "The Unfair Platformer"){kind=icon}
 "Mechanical Commando"){kind=icon}
 "Notessimo"){kind=icon}
 "The Egg"){kind=icon}
 "ButtonHunt 3"){kind=icon}
 "Portal: The Flash Version"){kind=icon}