This SO question has an open bounty of 400, but the questioner only has rep of 16. How is this possible? Perhaps, if the system allows you to offer two bounties of e.g. 400 when you have rep 416, and one answer is accepted, that would reduce your rep to 16, leaving the situation as described. How does SO prevent this kind of "bounty on credit"?
If an answer is accepted, how will the bounty be paid?