Some people claim they can cure warts with it.
Unfortunately, one of the things you can't do with duct tape is seal ducts. At least not for long, according to Max Sherman and Iain Walker of the Department of Energy's Lawrence Berkeley National Laboratory. Accelerated testing shows that fabric- backed tape with rubber adhesive tends to fall off. We tried as many different kinds of duct sealants as we could get our hands on. Of all the things we tested, only duct tape failed.