Unfortunately, by the time soliders recognized the existance of mustard gas on the battlefield, it would be too late to throw on a gas mask. However, Dr. Paul Bartsch discovered that slugs could respond to mustard gas far before humans could. Tests were run on dogs, but the gas would typically kill them before showing any physical signs of the gas. Slugs were found to show signs early on and slither away before they were killed. As the mustard gas would become present, slugs would show their discomfort by closing their breathing pores and compressing their bodies. They were placed in the trenches to help soldiers detect mustard gas. Soldiers in the trenches then could quickly put on their gas masks to protect themselves from the harmful gas in time. This discovery saved many lives.