It is observation of the performer's kind - a participatory observation, which is attuned to recognising specialities of behaviour across the spectrum of the physical and the social, which accepts and incorporates the environment as a influential theatre for human activity, and which is expert in physically internalising observed material for subsequent recapitulation. The observation itself is a practice, because it must be concealed, and it must be concealed because it is participatory. It is in the perfecting of the concealment that the observation takes place. As you do so, the environment you are attempting to merge with is informing you of attitudes, speeds, rhythms, dynamics, tensions, relaxations and habitual gestures. External information is matched with internal experiences.
Assimilation becomes understanding.
One might object that, for example. It gives no hint of the internal dynamics at work, the physical and social 'micro climates', where and how the various kinetic surges and impulses develop and dissipate. Without the participatory detail, we have a relatively neutral and unhelpful statement that 'such a flow exists' - not why it exists, what environmental pulls and pushes are experienced by the participants, what levels of energy and complexity are involved. We know the flow happens - but we have no inkling of what it is like and how the participants perceive and react to this environment. We cannot say whether such a flow represents pleasant or unpleasant situations and experiences.