Barney is the name of Olympia Myklos's pet cobra. As he is likely to sink his fangs into any visiting living creature, he is usually kept in a cage in Dr. Myklos' office.
Some time before 3:15 am, Barney is let loose by the murderer and bites Lavinia Waldorf-Carlton, losing one of his fangs in the process. After Laura Bow uses the snake oil and the snake lasso to capture him, he is returned to his cage.