You manifest thoughts by acting on them. Thoughts themselves don't create anything externally, but they can have an effect on your own body (placebo effect). The body can affect the mind, and the mind can affect the body. Thoughts can only affects your body, either internally, or to externally act upon your thoughts :) I haven't seen proof that it works any others way. Maybe some people allegedly can emit energy to heal people or whatnot, but that's using your body to produce something. We can't affect the external world simply by thinking as far as I know or can demonstrate. Speaking is an action, and words can affects others ;)