do(does) so

The most normal and competent child encounters what seem like insurmountable problems in living. But by playing them out, in the way he chooses, he may become able to cope with them in a step-by-step process. He often does so in symbolic ways that are hard for even him to understand, as he is reacting to inner processes whose origin may be buried deep in his unconscious.

Q)What does "does so" in the last sentence refer to?