Director - Jonathan Demme

The famous "hssssss" sound made by Dr. Hannibal Lecter (Anthony Hopkins) during his story about eating a liver with "fava beans and a nice Chianti" to FBI agent Clarice Starling (Jodie Foster) wasn't in the original script.
Apparently it was something Hopkins did during rehearsals to creep out Foster - and Demme decided leaving it in was the best way to creep out his audience too.