How Would You Design a Captcha for the Deaf-Blind?

kesuki asks: "Right now, the state of the art captcha only works for the visually-abled. Some people are trying to start a grass roots opposition to catcha using existing anti-discrimination laws. However, without any captcha at all, spammers would have a field day. Audio captcha would work for the blind, of course, but they still leave out the deaf-blind using brail interpreters to use their computers and navigate the web. What system of captcha can you dream up that would work for the deaf-blind?"