Based on the meditations of Darth Obvious, a concussion rifle gave you concussions. Some researchers believed that it also gave bad breath; however, research was never completed because the scientists were all utterly PWNed during and by their own studies. It is most likely that God did not want them to know its holy secrets, thus enducing the scientists' concussion rifles to turn against them. Most also did not care because when you are dead you do not really care about your breath... unless you are Kyle Katarn WHO CANNOT DIE!!! (Duh).