You may just come across this one throughout the main story, however, easily the best way to do this is on chapter 4.4 Defense with the Lurkers.
Just after you have defended against the Nosalis you come across a lot of Lurkers which don't do much damage and also don't take a lot of damage to kill.
Go through the opening to the second tunnel to trigger them then go back towards the way you came, back yourself into a corner and knife away.
When you can't hear any more growling move forward to trigger more in the next room and it is basically just a matter of time before the achievement pops.
You can also use this same method on 4.5 Child.