Biting

Biting is a common behaviour of closing the jaw found in many animals, including humans. Purposes include eating, harming, often to attack others, or sexual arousal. Some discussion of human biting appears in The Kinsey Report on Sexual Behavior in the Human Female.

Biting is also an age appropriate behavior and reaction for human children 30 months and younger. Conversely, children above this age are expected to have verbal skills to explain their needs and dislikes, as biting is not age appropriate. Biting may be prevented by methods including redirection, changing the environment and responding to biting by talking about appropriate ways to express anger and frustration. School age children, those older than 30 months, who habitually bite may require professional help.

https://en.wikipedia.org/wiki/Biting