A child with the anxious-avoidant insecure attachment style will avoid or ignore the caregiver – showing little emotion when the caregiver departs or returns. The child will not explore very much regardless of who is there. Infants classified as anxious-avoidant (A) represented a puzzle in the early 1970s. They did not exhibit distress on separation, and either ignored the caregiver on their return (A1 subtype) or showed some tendency to approach together with some tendency to ignore or turn away from the caregiver (A2 subtype). Ainsworth and Bell theorised that the apparently unruffled behaviour of the avoidant infants is in fact as a mask for distress, a hypothesis later evidenced through studies of the heart-rate of avoidant infants.