as a rear guard then the roles quickly switch. last in becomes first out. in realtime, it happens faster than i can describe and is repeated until all rooms are clear. once you've reached the last room, what happens then? >> back clear. >> reporter: in other words, do it again. just to be sure. the training has to be as real as possible which is why this woman does what we might consider crazy. volunteering to be a hostage, crouching in a room where the team will enter firing real ammunition at targets. just a few feet away. and this is the view if the hostage was you. the aim has to be perfect and it is. i think you can see the accuracy. and how does the team feel about snipers? but if a sniper has a shot is that the preferred -- >> absolutely. >> reporter: why?