For all the world this looks a little like an illustration by Arthur Rackham for a book of fairy tales. In fact it's the forest of stalks that support the oil-seed rape and next week the whole crop will be getting harvested by the combine.
When the two Jack Russells get into that forest they're gone for ages, because the field is supporting its own wildlife population: deer, pheasants, partridge, foxes, rats and rabbits to name just a few.
Never mind next week it will all have been de-forested, much to the terriers fury, but no doubt new opportunities for mischief and trouble will present themselves.