means To growl with bared teeth, or to speak in a low, angry, threatening way — and, separately, to tangle something into a knotted mess.

from Two strands twisted together here. The growling 'snarl' comes from an older English 'snar,' related to words across the Germanic family for snorting and grumbling — think of the nasal 'sn-' cluster that English keeps for unpleasant noises (snore, snort, sneer, snarl). The tangling 'snarl' is a separate word, a diminutive of 'snare,' from Old English 'snearu' (a noose or cord), with cousins in Old Norse 'snara' — so a snarl was literally a little snare, a small entrapping tangle. Over time the two meanings sit comfortably side by side, both suggesting something caught and bristling.