I have found on many levels some people have a Frag on their side level 4 as Major said had 3 for me and 5 had 3 for me as well as 7 if you see a Guy with a frag then all you need to do is sneak up like normal and then instead of A to kill you press B and run away. Also, I want to confirm that you can not die and Reload checkpoint i have gave this a shot no luck. So over the course of the game you need to do this five times. You could always save it for last and load level 4 and start from there!