Snarl

A snarl is a facial expression

Facial expression

A facial expression results from one or more motions or positions of the muscles of the face. These movements convey the emotional state of the individual to observers. Facial expressions are a form of nonverbal communication...

, where the upper lip is raised, and the nostrils widen, generally indicating hate, anger

Anger

Anger is an emotion. The physical effects of anger include increased heart rate, blood pressure, and levels of adrenaline and noradrenaline. Some view anger as part of the fight or flight brain response to the perceived threat of harm...

 or pain

Pain

Physical Pain is the unpleasant feeling common to a headache and a stubbed toe. It typically consists of negative affect and aversion, and has location, duration, intensity and a distinctive quality...

. In addition to human

Human

Humans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...

s, other mammal

Mammal

Mammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...

s including monkey

Monkey

A monkey is any cercopithecoid or platyrrhine primate. All primates that are not prosimians or apes are monkeys. The 264 known extant monkey species represent two of the three groupings of simian primates...

s and dog

Dog

The dog is a domesticated form of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history...

s snarl, often to warn others of their potential bite. In humans, snarling uses the levator labii superioris alaeque nasi muscle

Levator labii superioris alaeque nasi muscle

The levator labii superioris alaeque nasi muscle is, translated from Latin, the "lifter of the upper lip and of the wing of the nose". It has the longest name of any muscle in an animal.- Attachment :...

. Snarling is often accompanied by or used synonymously with threatening vocalization

Vocalization

Vocalization, or vocalisation , may refer to:*Speech communication*Vocal music*A type of animal communication involving their vocal cords...

s (it may also be used as an onomatopoeia

Onomatopoeia

An onomatopoeia or onomatopœia, from the Greek ὀνοματοποιία , is a word that imitates or suggests the source of the sound that it describes. Onomatopoeia refers to the property of such words. Common occurrences of onomatopoeias include animal noises, such as "oink" or "meow" or...

for a threatening noise, as in the 'snarl' of a chainsaw).