Arc mines are one of the new weapons in this DLC. The earliest you can do this is in the first mission. All you need to do is find an arc mine and throw it on a rat. When a guard (or any other character, civilians included) walks next to the rat, the arc mine will vaporize them. Make sure to make a quick save before you place the mines, just in case the rats don’t get close enough or the enemy kills you before they kill the enemy. If you’re having trouble or want to see it done, please refer to the video below.