It is free and universal. Certain situations, however, facilitate it. A Zen master will sometimes move among his meditating students. With his sharp intuition he knows who is sleepy and distracted and gives the student a rap on the shoulders. Nothing aggressive, just a reminder to be aware.
Children do the same thing without knowing it.
Their cries, their questions and demands, are a continuous recall to the here and now, to where all is more real. Our very own place. Very young children are always in the present. They reside there with ease and with wonder. His eyes move imperceptibly.