A couple of things from Tanya's research.

When discussing with Kelly why she kept pictures of attack victims, Tanya said that she was searching for the Zs attack patterns. She suggests that they go for the neck first with the highest frequency. This can be interpreted in at least two ways.
1) They are trying to kill their victims quickly with little struggle or before thy turn into a zombie and the neck is the fastest way to do this.
OR
2) Since victims suffering neck bites were more likely to die as opposed to turning, most of the dead available for photos were killed in this manner.

Tanya may have stumbled onto the notion that Ink is conserving his Inklings by getting the Colonists to use up their ammo first. Someone mentioned this strategy in another thread and I apologize for not remembering who. But now, our heroes are becoming aware of this.