(Image credit: Universal Pictures) The weirdest thing about "Slither" is not so much that James Gunn made it. It's more that the writer/director of this schlocky, unashamed B-movie went on to make a trio of "Guardians of the Galaxy" movies and "The Suicide Squad", before being installed as the head of DC Studios and bringing " Superman " back to the big screen. How many of Hollywood's biggest names have alien worms on their resumés? Violent, gory, and often played for laughs, "Slither" was always an outlier among the big-budget blockbusters and torture porn that dominated the mid-'00s. But, rewatching the film 20 years later (March 31 was the actual anniversary), Gunn's fingerprints are unmistakable, from the highly quotable dialogue to the quirky soundtrack lifted from the outer reaches of Gunn's eclectic music collection. Article continues below (Image credit: Universal Pictures) But screenplays were never his final goal.…