LOS ANGELES (Reuters) - Sex was an endless topic of conversation for the characters in director Kevin Smith’s 1994 breakthrough hit “Clerks,” but in his new movie “Zack and Miri Make a Porno,” sex is more than talked about, it’s on display.

The director of "Zack and Miri Make a Porno" , Kevin Smith, attends the premiere of the film in Los Angeles October 20, 2008. REUTERS/Phil McCarte

“Zack and Miri Make a Porno” debuts in theaters on Friday and is likely to be labeled as Smith’s most sex-filled movie yet in a career that is long on topics of sex, raunchy humor and scatology.

His 1997 film “Chasing Amy” tells of a woman who had sex with two men. “Dogma” (1999) has a demonic character made of excrement. In “Clerks,” a woman mistakenly has sex with a dead man in the dark and its sequel, 2006’s “Clerks II,” features a show involving a donkey -- enough said.

Still, Smith told Reuters in a recent interview that sex is not the point in “Zack and Miri.” Love is. The director uses sex as a way to explore human lives and relationships.

“For me, a character is fully explored when you can really get your head around them, when you know a bunch about them,” Smith said. “And there’s no better way of knowing a person than knowing what their sex life is.”

Zack and Miri (Seth Rogen and Elizabeth Banks) are not porn stars -- at least not until their dead-end jobs leave the platonic friends with no electricity or running water in the apartment they share in frigid Pittsburgh.

So, they enlist the help of some eager exhibitionists to make an amateur porn movie they believe will earn them enough money to lessen their predicament.

Zack and Miri promise each other that having sex on camera will not ruin their friendship, but making a porno movie proves to be more emotionally complicated than they expect.

“The movie definitely lives up to its title. Zack and Miri do indeed make a porno,” Smith said. “But that being said, the movie’s not really about it.”

“PORNO” TOO HOT?

Still, it took some convincing to get the Motion Picture Association of America to see the movie the way Smith does. The MPAA represents major Hollywood studios, and its ratings are used as a way to classify the content within a film.

In the case of “Zack and Miri,” it was initially rated “NC-17,” which means no children 17 years-old and under are permitted. Very often that rating has swayed some viewers and advertisers to think a film is, in fact, pornographic, even though it is not in the eyes of the MPAA ratings board.

Smith agrees some scenes “push the edge of the envelope” as to what could be considered porn, but he appealed the rating. Eventually, it was reduced to “R,” which means people 17 and under can see it if they are accompanied by an adult.

Rogen, 26, fresh off the success of his marijuana-themed summer hit “Pineapple Express” and the 2007 sex comedies “Knocked Up” and “Superbad,” -- all rated R -- said he never understood why “Zack and Miri” almost received an NC-17.

“I honestly feel like if people saw it they would have been like, ‘This is NC-17?’” Rogen said. “And they would have been disappointed...I know enough about movies to know we’re not doing anything that hasn’t been done in movies rated PG-13.”

Advertising the film, which is being released by The Weinstein Co, has proven tricky.

Officials in Philadelphia, for instance, declared their bus stops off-limits to ads because the film’s story involved pornography, and TV spots are airing as just “Zack and Miri” without “make a porno” being spoken along with the title.

“I’m stunned that people have that big of an objection to the word,” Smith said. “Porno is not a bad word, it’s a word that describes something. It’s a word that describes a genre or a field of filmmaking,” he said.