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For the most part, dolls are, as stated, passive mediums, lacking any emotional response patterns not programmed in (at one point in the second season, July (MI6's doll who sees through glass) says "smiling is not in my program" when told to do so.)

However, Yin's case seems to indicate that with sufficient stimulus of life as a normal human, pieces start to come back, as they did for Yin about 2/3 of the way through Season 1.

As yet, the topic of dolls has not been fully explained.