When you like escape from a level in reach by crouch jumping or what ever you can walk for a while and find a small covenant group.
The grunt is being punished by an elite.
When the grunt sees you he will run towards you and say: ´demon, save me please please please´ and he will hug you and hold your leg like a little kid.
If you kill the elite the grunt will be your pet/ally (as long as you can keep him alive)