The Horse Head Incident
This scene is easily one of the most talked-about (and the most disturbing) from The Godfather series. The Corleone's placed a horse's head in Jack Woltz's bed. Most viewers would assume that this was just some Hollywood effects...
It Was Real
Sadly, that was not the case. The blood itself was fake, but the horse's head was absolutely real. This factor just added to the creepy suspense!