Vaults can be hollow.Logical formLearned from5 sentences. (Metal frames) can be hollow.Logical formLearned from5 sentences. A trail can be hollow.Logical formLearned from5 sentences. A compartment can be hollow.Logical formLearned from5 sentences. A pyramid can be hollow.Logical formLearned from5 sentences. A mast can be hollow.Logical formLearned from5 sentences. Sacs can be hollow.Logical formLearned from5 sentences. A historic district can be hollow.Logical formLearned from5 sentences. An interior can be hollow.Logical formLearned from5 sentences. A (campaign setting) can be hollow.Logical formLearned from5 sentences. Pseudobulbs can be hollow.Logical formLearned from5 sentences. A (metal pipe) can be hollow.Logical formLearned from5 sentences. (Glass beads) can be hollow.Logical formLearned from5 sentences. A (shaft drive) can be hollow.Logical formLearned from5 sentences. An edge can be hollow.Logical formLearned from5 sentences.