Rocket has expressed interest in having the infected to be in certain "stages" of infection recently. What about the idea of implementing that the freshly infected have good use of limbs which help them run and chase at high speeds, but body shots can still put down the freshly infected. Meanwhile, zombies in the later stages of the infection would have poor use of their host body, but due to the complete takeover of the infection, a headshot is required to put it down for good. With that, it satisfies the want for different kinds of zombies, gives purpose to the different stages of the infection, and adds a different element to determining the best way to handle the infected in your path. I use the words "zombie" and "infected" interchangeably because I don't care and it's silly to argue it. It's clear what my point is, so lets not whine over the technicalities.