Call of Duty: Modern Warfare 2
51 Achievements
27-33h
Knock-knock
Kill 4 enemies with 4 shots during a slow-mo breach in Single Player or Special Ops.
15.2%
How to unlock the Knock-knock achievement in Call of Duty: Modern Warfare 2 - Definitive Guide
A slow-mo breach is when you breach into a room with the flat white wall explosive. Nearly every breach in the game will give you an opportunity to earn this trophy. But it van be most easily earned in the mission ‘The only easy day was yesterday’. You will breach several rooms in this mission, but the room in the video below is the easiest. Go through to the room, and set up to breach on the left door. As soon as you go through, pick off the enemies from the left to the right, one bullet each, aiming for the head each time. Restart the checkpoint if you fail. Credit to NextGenTactics for the video.
https://www.youtube.com/watch?v=xqhc61elWqQ
A slow-mo breach is when you breach into a room with the wall explosive. The best way to get this achievement is to play Special Ops mission called Breach and Clear. Switch to your M203 grenade launcher by pressing and breach the wall. Once you are in slow mo, fire a at the group of people that is a directly in front of you down the hall.
You can also follow this video by Mistical: