Areas can be hollow.Logical formLearned from40 sentences. Doors can be hollow.Logical formLearned from40 sentences. Chambers can be hollow.Logical formLearned from39 sentences. Sounds can be hollow.Logical formLearned from39 sentences. An expedition can be hollow.Logical formLearned from38 sentences. A voice may sound hollow.Logical formLearned from38 sentences. A rock can be hollow.Logical formLearned from38 sentences. A life can be hollow.Logical formLearned from38 sentences. Words may sound hollow.Logical formLearned from38 sentences. Cores can be hollow.Logical formLearned from37 sentences. A noise can be hollow.Logical formLearned from37 sentences. A (tree trunk) can be hollow.Logical formLearned from36 sentences. Balls can be hollow.Logical formLearned from36 sentences. Bodies can be hollow.Logical formLearned from36 sentences. An army can be hollow.Logical formLearned from35 sentences.