The first cry is a defensive emotional expression, a message that something is amiss. Researcher S. Bowlby sees this cry as an instinctive signal that releases behavior. A mother learns to interpret her child’s cries within days. For example, a cry of pain is unmistakable and impels a caretaker to respond immediately. The cry of fear does not appear unit about seven mounts. The expression of fear is a function of mental growth. This can be seen in the progression of factors that trigger the fear response. At first, physical sensations, such as sudden noises or a loss of support, are necessary. Later, the perception of heights or strangers will suffice. Finally, the dark, now filled with mental creatures, can elicit fear.