A fill can be hollow.Logical formLearned from17 sentences. Rods can be hollow.Logical formLearned from17 sentences. Branches can be hollow.Logical formLearned from17 sentences. A character can be hollow.Logical formLearned from17 sentences. A groan can be hollow.Logical formLearned from17 sentences. A result can be hollow.Logical formLearned from17 sentences. A room can be hollow.Logical formLearned from16 sentences. Caves can be hollow.Logical formLearned from16 sentences. Waves can be hollow.Logical formLearned from16 sentences. Beads can be hollow.Logical formLearned from16 sentences. A valley can be hollow.Logical formLearned from16 sentences. Tiles can be hollow.Logical formLearned from16 sentences. A talk can be hollow.Logical formLearned from16 sentences. (Metal tubes) can be hollow.Logical formLearned from16 sentences. A story can be hollow.Logical formLearned from16 sentences.