English Language · Reading Comprehension

Read the given passage and answer the question that follows: After breakfast, Jack walked to the post office. I took the one-eyed collie to chase rabbits in the upper fields, but it barked at ducks and brought me a tramp's shoe from a hedge, and lay down with its tail wagging in a rabbit hole. I threw stones at the deserted duck pond, and the collie ambled back with sticks. Jack went skulking into the damp dingle, his hands in his pockets, his cap over one eye. I left the collie sniffing at a molehill, and climbed to the tree-top in the corner of the field. Below me, Jack was playing Indians all alone, scalping through the bushes, surprising himself round a tree, hiding from himself in the grass. I called to him once, but he pretended not to hear. He played alone, silently and savagely. I saw him standing with his hands in his pockets, on the mudbank by the stream at the foot of the dingle. My bough lurched, the heads of the dingle bushes spun up towards me like green tops. 'I'm falling!' I cried, my trousers saved me, I swung and grasped, this was one minute of wild adventure, but Jack did not look up and the minute was lost. I climbed, without dignity, to the ground. Two words describe how Jack played alone. What are they?