Flooding involved exposing a person with a phobia with the phobic object without a gradual build-up.
A person with arachnophobia receiving flooding treatment may have a large spider crawl over their hand until they can relax fully.
Very quick learning through extinction
Without the option of avoidance behaviour, the person quickly learns that the phobic object is harmless through the exhaustion of their fear response. This is known as extinction.
Ethical safeguards
Flooding is not unethical but it is an unpleasant experience so it is important that people being treated give informed consent. They must be fully prepared and know what to expect.