This is semi-common sense:
In a previous patch, a feature was added. When you were sitting, you would be auto-crit by an attack.
Me and a few friends were in a zombie raid, and we needed our newcoming friends dead a lot faster then we would normally.
And thus, they tapped the "x" button while we attacked.
We brought fourth a new meaning to "Crit your pants."
Summary:
In order to become killed faster by your zombie allies:
Get infected (By their attacks or otherwise)
Spam the "x" or your key bound sit button.
Have your friends attack you until dead.
Be a zombie.
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Good luck!