In the Lower East Quack level, go past the area where you hitch a ride on the subway train. Go to the end where you see a brown fence and a little hole at the lower left side. When you are there, turn left to find a Chang transport. Once you are Chang go though the hole, and on to the boxes. Chang will start scratching himself all over. You will then be transported on his back as a flea with a heavy-machine gun.