In the opening sequence, when Mary Ann & Ginger are seen running from the natives, Gilligan is putting up a large SOS sign made of canvas. When Gilligan finally sees who the girls are running from, he does so as well, running directly into the sign & falling backwards, with the sign landing on top of him , covering all but his feet & lower legs. The natives continue pursuing the girls , each stepping on Gilligan in turn. In watching the feet & legs, it can be clearly seen that Bob Denver has been replaced by a dummy.