Cletus is a character on the T.V. show
The Simpsons. Cletus is a stereotypical stupid poor hick.
Buffy: Ok, be kind.
Rewind.
Buffy asks her friends to repeat themselves by evoking the video store
mantra. Almost every video rental store has a "Be
kind. Rewind." notice to remind patrons o rewind their videos before
they are returned.
Buffy: I'm thinking weird
science.
Probably a reference to 1985 movie
Weird Science. In the movie a couple of nerdy
boys manage to create the perfect woman with a combination of science and
magic. About the only relation to the episode is that in the movie there
are also scenes with lots of junk strewn about.