What does it mean to “sniff at someone?”

Question

The book series "The Wheel of Time" frequently talks about characters "sniffing" at someone.

Here are a few examples:

“ ‘Poke the meekest dog too often,’ “ Elayne quoted, “ ‘and he will bite.’ Not that Lan is very meek.” She got a sharp look and a sniff from Nynaeve.

Or this one:

Her smile became a grin that made Elayne sniff disapprovingly

It doesn't seem natural to think of someone inhaling air through their nose in these situations... So what does it really mean?

Answer 1

A sniff (drawing air through the nose in a short, audible inhalation) is sometimes used as a sign of contempt. See Dictionary.com:

4. to show disdain, contempt, etc., by or as by sniffing.

Nynaeve is disparaging Elayne's comment by the sniff. Note that a sniff can be a haughty way to express disdain, as if words would be too much to waste.