ZNS- Kill 3 mutating zombies??

[Kipstarjones187 0]

I came across a challenge where you have to kill three zombies that are mutating, I used the spores and killed one... Trying to repeat the step again, and the orange mist is going around the zombie but I haven't been able to kill the other two... Anyone know when to shoot? Did it three times and wasn't able to replicate the first kill.

[jaysta5792 11]

You have to kill them as they are going into the ground. It's a small window of time, but easy enough