In Judith Minty's "Conjoined", what does the onion mean?

epollock | Student
In the figures of the onion, the twins, and the calves, the three were intended to be separate, but instead they are freaks of nature, accidents that allowed them to live but to live abnormally. The speaker suggests that this situation is like marriage. In lines 12–13, the speaker indicates that freedom (divorce, separation) might kill one partner, as it sometimes kills a Siamese twin. Note that the one who might not survive is not specified. The metaphor thus represents recognition of reality and both a reluctant concession and a decision to adjust. An increasing number of men now “slice onions,” but men, more often in charge of power and money, usually lay out the grounds of a relationship. Hence it is often asserted that women must be alert to hidden dynamics (body language, looks) to protect themselves emotionally, while men may be more direct and less subtle.