Just after sunrise the otters line up under the little park bridge, each with a round stone held as carefully as a bun from the bakery.
We asked at the kiosk by the path. A man waiting for cocoa said the class is very strict and very kind. An otter greets the water first, waits for the willow to nod, and only then rolls the pebble once across its belly, slow enough that the ripples can take notes.
The park keeper pinned a damp card to the railing: enrollment is one smooth circle. The willow, he wrote, has agreed to nod only once, so nobody has to guess when the lesson is over.
By the next morning a single pebble was drying on the bank, still faintly warm, as if it had been congratulated and sent home for tea.