Remember how the ‘foam finger gun’ was one of the secret weapons that you can get in Dead Space 2? If you somehow missed that weapon, you will have an opportunity to get it again in Dead Space 3.
To get the gun, simply complete the game in Classic mode under the New Game + play through. Once you do, you will unlock one of the game’s most powerful weapons where it can kill any enemy in just one shot. You’ll also hear Isaac say ‘bang’ and ‘pew’ with each shot.