So when I get bit by a zombie, whether it be the intentional bite you take or any accidental bites along the way, I always take 3 munches. However, the faster runners seem to only take 2.

I've been told by one person that you mash action, told by another that you mash left and right, and told by a third that you mash all buttons to get zombies off you faster. Nothing seems to work for me though, I always get stuck taking 3 munches.

Is there any definitive way to guarantee only 2 munches from a zombie?

i used to mash WAD(whatever movement keys you feel comfy) aim and action

The more you mash those and the faster you start mashing, the more likely to shake off in 2 bites.

Yup, like others have said I believe it's left, right, action and run/cancel that you mash to break the grip faster.

Maybe aim works too but I can confirm I break in two bites consistently and I don't mash aim.