Apparently there were subliminal messages placed in Alfred Hitchcock's 'Psycho'. What did they say, and where were they placed?

Hidden Persuaders by Vance Packard could be found on the reading lists of many high schools in the late 1960's. This book was highly discredited by its opposition when it was published in 1957. This book published numerous case studies of subliminal messages that had obvious observable results. Packard quoted a London Sunday Times issue in which a New Jersey theater claimed that ice cream sales soared due to the flashing of ice cream ads on the movie screen in what was called a "subthreshold effect."
https://en.wikipedia.org/wiki/Vance_Packard#The_Hidden_Persuaders


Packard later asserted that the words blood, knife, and murder were used subliminally in Alfred Hitchcock's famous movie Psycho to heighten fear in his audience.

A more obvious example is a human skull, when they zoom in on Norman Bate's face at the very end of the film, right before they cut to the car being towed from the swamp.

http://subliminalmanipulation.blogspot.com/2010/09/other-uses-subliminal-content-doesnt.html