Successive experiments concluded that infants used the surrogate as a base for exploration, and a source of comfort and protection in novel and even frightening situations.  In an experiment called the "open-field test", an infant was placed in a novel environment with novel objects. When the infant's surrogate mother was present, it clung to her, but then began venturing off to explore. If frightened, the infant ran back to the surrogate mother and clung to her for a time before venturing out again. Without the surrogate mother's presence, the monkeys were paralyzed with fear, huddling in a ball and sucking their thumbs.