 Alfred Hitchcock (I) (qv) originally planned to do his cameo as  the body floating in the river. A dummy was even constructed to do  the shot. The plans were changed and a female body, a victim of the  Necktie Murderer, was used instead. Hitchcock instead became one of  the members of the crowd who are listening to the speaker on the  river bank. The dummy of Hitchcock was used in the typically  humorous trailer hosted by Hitchock himself.