The study in this paper belongs to the field of the grammar of metaphor. Six types of animal words were investigated in order to find the connection between their parts of speech and metaphorical relationship by applying the British National Corpus in combination with Collins Dictionary. It is found that not all verbs formed via conversion from nominal animal words carry the conceptual features of the animal entities, and in this case, the resultant verbs do not form metaphors. Where the verbs carry over the conceptual features of the nominal animal words, metaphors will occur. Of course, there are a few exceptions, like fish in fish for, which forms a metaphor though fish as a verb here does not carry over the conceptual features of the nominal fish.As to adjectives and adverbs derived from nominal animal words, they form metaphors in most cases by carrying over the conceptual features of the relevant animals. The study can be broadened to other entity nouns in order to find regularities about when their derivatives form metaphoricity.