I bought this asset but I'm not finding the file with the animation of the zombie's head being cut off, as shown in the second image
Sorry, nearly missed this message.
When we tried the sprites before release we made that with some help of code, just cutting out the head and then make it fly away. More dynamic so it can react to other objects. We didn't feel it would look good just adding a static animation.
I would recommend that or even cutting out more parts + adding the blood explosion-animation on top + red pixel particles flying out. It will look amazing :)