To breathe air quickly through the nose to smell something, or to show contempt or disdain.
From Old Norse 'snjófa' and Germanic roots imitative of the sound itself. The word is onomatopoetic, imitating the actual sound of sniffing.
Your sense of smell is ten thousand times more sensitive than your sense of taste, so when you sniff food before eating, you're actually doing most of the work of 'tasting'—which is why food tastes boring when you have a cold and can't sniff properly.
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