Load Chapter "Cathedral of Resurrection" from Episode 1, after 2-3 Minutes in the Chapter you jump out of a Window and standing in an alley.
Here is a Checkpoint, go forward and activate the Zombies, the Suicide zombies running towards to you, use now Focus Time and try to shot the Grenades in the Hand of the Suicide Zombies. If you failed, reload the Checkpoint. If you want you can also here boost the "We don't need a stretcher. We need a mop!" (At least 50 Suicide Zombies denied) Achievement.