Mr Roberts, headteacher of Maesmawr School, Welshpool, takes his charges for a walk in nearby fields. Sheep dog ‘Patsy’, belonging to the film-maker Ion Trant, keeps an eye on them all. They find rosehips, and also oak apples or galls which Mr Roberts later dissects. The gall without a hole holds a grub, a wasp larva. A small hole in another indicates that a grub has already tunnelled its way out; a large hole in a third indicates that a bird has pecked out the tasty grub within.