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Signs of depression include feeling sad most of the time for 2 weeks or longer; loss of interest in things normally enjoyed; lack of energy; sleep and appetite disturbances; weight changes; feelings of hopelessness, helplessness, or worthlessness; an inability to make decisions; and thoughts of death and suicide.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
The familiar sounds of your heart are made by the heart's valves as they open and close.
Pubic lice (crabs) are usually spread through sexual contact. You cannot catch them by using a public toilet.
Of the estimated 2 million heroin users in the United States, 600,000–800,000 are considered hardcore addicts. Heroin addiction is considered to be one of the hardest addictions to recover from.