What is "sssssss"

Sssssss (released as Ssssnake in the UK) is a 1973 horror film starring Strother Martin, Dirk Benedict, and Heather Menzies. It was directed by Bernard L. Kowalski and written by Hal Dresner and Daniel C. Striepeke, the latter of whom also produced the film. The make-up effects were created by John Chambers and Nick Marcellino. It received a nomination for the Best Science Fiction Film award of the Academy of Science Fiction, Fantasy & Horror Films in 1975.