A dead body can't smell. Zombies don't acknowledge each other or "High 5".
Whatever makes them go after live bodies (electrical impulses from our brains, faster moving targets or motion in general, etc) has nothing to do with Zombies telling Zombies apart. They don't recognize each other.
If that were the case, you'd see Zombie families gathering for snacks in the park.
They seem to not actually know that other zombies exist other than fallowing the moans that tell of fresh food. I think it's more how the notice people. Theory's suggest that it's because of the smell of all of the consumer products we use. Another would be the way we move...