Figurative language would be the best answer for this question. Figurative language is the opposite of literal language; here, the speaker is not saying that Ismene is a literal snake, sucking out the life from him. He is using a metaphor to tell her that he thinks she is being sneaky, deceptive, and destructive. That is what figurative language means: using words that the speaker does not literally mean to convey a point. Hope this helps.