At the end of their first session, the therapist sent Mandy home with an assignment: Carry around an index card, and each time you feel the cue — a tension in your fingertips — make a check mark on the card.
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Then the therapist taught Mandy what is known as a “competing response.” Whenever she felt that tension in her fingertips, he told her, she should immediately put her hands in her pockets or under her legs, or grip a pencil or something else that made it impossible to put her fingers in her mouth. Then Mandy was to search for something that would provide a quick physical stimulation — such as rubbing her arm or rapping her knuckles on a desk — anything that would produce a physical response.
The cues and rewards stayed the same. Only the routine changed.
They practiced in the therapist’s office for about thirty minutes and Mandy was sent home with a new assignment: Continue with the index card, but make a check when you feel the tension in your fingertips and a hash mark when you successfully override the habit.
A week later, Mandy had bitten her nails only three times and had used the competing response seven times. She rewarded herself with a manicure, but kept using the note cards. After a month, the nail-biting habit was gone.