The poem opens with a question that sounds almost helpless: how can anyone truly know all of their own habits? The speaker treats habits as "strange creatures," living things that stay close and even carry "a kind of love." That phrase is a little odd and a little tender. Habits aren't enemies here; they're companions we feed without thinking.
The oysters make the idea concrete. They "eat to understand," and the water they take in is "a spice," so their understanding comes through repetition, simply by living in what surrounds them. Habit becomes a way of knowing the world, though not a deliberate one.
The last lines are the most puzzling. A surgeon and his wife "work in my bed," which suggests something intimate, careful and slightly clinical, though the poem doesn't explain it. Judging by the imagery, the speaker may be picturing habits as things that cut into private life. The mood is dreamlike, curious and quietly unsettled, with affection mixed into the strangeness.