I disagree with most everyone - I don't think it is a good idea to do what you want without considering your husband's opinion - I think it is a mistake to get a snake and then expect him to 'forgive your decision'. In my opinion, marriage is about discussion and agreement before a major decision, and about considering the other person's concerns and desires, not discounting them. I don't believe you mentioned feeling you needed his permission (I agree you are not a child), but you wanted to have him consider your request.
Aquiring any animal is a long term decision, and even if one partner is primarily responsible, it will have an impact on the other. I think it is up to you to decide how important having a snake is to you, and if it is critical to your happiness, then find a way to help him understand how much and why it matters to you. It would help if you can to be prepared to see his point of view as well, understand his reasons for not wanting one.
Based on my experience, people want their partners to be happy and want to help make them happy. If they realize how much a little thing, like your pet snake, would bring great happiness to you, they will be more willing to support you. Of course, it works both ways - always the challenge of compromise.
Though I appreciate the humor of some of the responses, in my opinion, there is never a good reason to manipulate your spouse. Good luck in deciding what you want to do,