Infoplease defines aggression as behavior that can be directed toward others or internally, and which can be either constructive or destructive. Humans are certainly not alone in expressing aggression against one another. However, aggression in human beings is often motivated by factors beyond physical survival. In many cases, human aggression is not manifested in any physical way.

Physical aggression often involves acts of violence taken with the intention of causing harm to the recipient, including death, by using weapons or even someone's bare hands. Anger is a frequent source of aggression, but aggressive behavior can also result from intoxication or frustration, according to Wrong Diagnosis and Healthy Children. People suffering from Alzheimer's disease may also manifest aggressive behavior as a result of diminished cognitive capacity, confusion or frustration, according to Healthy Place. Self-mutilation, or physical violence turned against oneself, often occurs in conjunction with serious mental disorders, such as borderline personality disorder, according to the National Institutes of Health and the Associations to Assist Persons With Emotional Lesions as well as antisocial personality disorder, according to OpenMed.

The children's taunt "sticks and stones may break my bones but words will never hurt me" fails to account for emotional abuse carried out through verbal hostility. Verbal aggression includes behavior such as bullying, threats or yelling. The Mayo Clinic includes name-calling and insults under the category of domestic violence. Put-downs, intentional or perceived, can have profound detrimental effects on the recipients. Musician Karen Carpenter reportedly became anorexic after reading a review that called her "chubby." She died in 1983 of complications from anorexia nervosa at only 32 years old, according to Queen City News and OC Weekly.

Nonverbal intimidation often implies the threat of violence, at least in the perception of the person at the receiving end. Stalking often involves one or more forms of nonverbal intimidation, including following the victim, planting malicious software in a victim's computer, sending unwanted gifts and vandalism against the victim's property, according to Sexual Harassment Support. A famous example of nonverbal intimidation occurred during the movie "Fatal Attraction," when Alex kills her victim's daughter's pet rabbit.

The Mayo Clinic defines passive aggression as an indirect way of expressing displeasure or anger. Passive aggression is often generated by resentment on the part of someone who is unable or unwilling to express this resentment directly. Deliberately or subconsciously performing a task poorly is one form of passive aggression, agreeing to perform a task but failing to do so is another, according to Psychology Today. Procrastination can also be a form of passive aggression.