How do you get the ray gun in Call of Duty 5?

on the second level on the beach, you have to go to the far puddle to the right and the walk and crouch in each puddle towards the left. when you reach the final puddle, start crouching and moving around in the puddle until the screen starts rumbling. dragon heads should pop up. you should then go to one of the heads and press x/sqaure, and you will then get the ray gun.