[Frail]

When Kellhus is studying the-thing-called-Sarcellus in TWP it brought up a question that I don't think is answered in the books. Kellhus can see skin spies almost immediately because they have no face, and he can notice the false expressions given out by the creatures, but as far as I know he cannot smell the difference as Aurang does when he finds the previous skin spy Sarcellus at Mengedda.

So how do other skin spies tell apart one another from men? I know the captured one during TTT screams in a high pitched voice that "only rats can hear" but I would be curious how long it would take a skin spy to find his brother in a crowd of people.

[Madness]

Well, one, they aren't supposed to socialize .

But yeah, I mean, you've highlighted two and I'm sure the Consult can exploit a whole spectrum of behaviors that broadcast at thresholds unavailable to humans.

[Monkhound]

Was there not a thing where skin-spies could recognise people and others by smell?

[Wilshire]

Was there not a thing where skin-spies could recognise people and others by smell?

Yeah both times they are hunting Kellhus they mention smell several times.

[H]

Aurang actually has grafts that enable him to give off, and presumably detect, pheromones.

It's plausible to thing that some that the skin-spies give off could simply be outside human perceptual range, or simply the difference could be smaller than the just-noticeable-difference. 

Then again, perhaps Dûnyain smell simply isn't all that more advanced than human?  Or just not enough to tell.