The people Zack remembered best, he remembered them by their scent.
The Turks were generally a clean smelling bunch, with just the slightest hint of blood around them. Except for Reno, who reeked of beer and cigarettes.
Angeal smelled of mako and sword polish, with a hint of apples underneath. Until the end, where he smelled of nothing by mako and despair. In contrast, whenever he's around Cloud, Zack's reminded of mountain pines and fresh rainwater.
Sephiroth smelled of mako, leather and sword polish. Until Nibelheim, where his scent was overlaid by madness and the smell of burnt dead things.