This chapter introduces the mechanisms behind the theory of opposite action, showing how changes in the brain and body are bi-directional, how changes made in the body can influence the intensity of emotion, and how the intensity, in turn, can influence the body. Making changes in any of the domains changes the emotional experience by a notch. The more domains in which the therapist is working, the more the emotion is likely to change. The chapter introduces examples of behavioural chain and solution analysis, of target behaviours that are tracked on a diary card. The author gives a rationale for analysing past events for their rich contextual data, rather than having clients rehearse for upcoming situations. Two client scenarios are scripted with the therapist interventions labelled so the reader can see what each exchange is designed to accomplish.