Video of a miracle, or if you prefer, magic using ritual and the spoken word and relics.
Of course, a skeptic will automatically react to this ("the water had salt, then they changed it, the surface tension was broken, etc., etc." or even worse, they switched the fragment, or it isn't wood but some other substance, etc."). The Cartesian mind can always find an alternative explanation (psychologists should realize that "rationalization" is a mental, not a scientific, operation). And of course, there is the possibility that charlatans can perpetrate a hoax; however, to reject the possibility outright, or to suggest that it is done with the power of "demons" (this might be the Protestant approach for the hard-core "evangelical"), is to effectively assert (from the lesser to the greater) that miracles do not occur anymore. Is this where modern Christianity is arrived? What have we come to? God is a God for the living, not the dead.