(Gravity dams) can be hollow.Logical formLearned from1 sentences. Branches can be in hollow trees.Logical formLearned from1 sentences. Some bones of (adult birds) can be hollow.Logical formLearned from1 sentences. (Metal bells) can be hollow.Logical formLearned from1 sentences. A (ring wall) can be hollow.Logical formLearned from1 sentences. Bats may inhabit hollow trees.Logical formLearned from1 sentences. (Bird bones) can be hollow.Logical formLearned from1 sentences. A tube can be hollow.Logical formLearned from1 sentences.