To snarl or make a snarl is to growl like an angry dog or speak abruptly and aggressively. A snarl can also be something tangled or confused.
If you've ever heard a dog growl, then you know what a snarl is: a dog's snarl says, "Back off!" When people snarl, they speak in an angry way that isn't shouting but sounds mean. A human snarl is abrupt, sharp, and unfriendly. Another sense of the word is when something gets mixed up, like if wires get tangled together: that tangle is called a snarl. This meaning comes from the earliest use of snarl, "a snare or a noose."