Is it any wonder? Generally, the situations where you would actually become intimately familiar with the smell of someones hair are, well, intimate.
Eh, not really. If someone were to use a kind of shampoo that has a really noticeable scent (like say for example, a lot of girls and women) it's not too hard to notice. It might be hard to distinguish between shampoo and perfume, but I guess that's not really the point. If you're walking side-by-side a lot like these two seem to do, it makes sense that the other person would notice at some point.
Y-you lecher!!WHA-?!We're always hanging out together, why would it be so weird that I catch the scent!ClonkLike hell!!Have you been sniffing me all this ti-GHACKI wonder if he'd notice if I changed my shampoo...It smells nice, too.