Monsters come in all shapes and guises in the cinematic universe of South Korean director Bong Joon-ho.

In his 2003 "Memories of Murder," the monster was a serial killer whose murders were never solved by the police. In his acclaimed 2006 "The Host," which holds the record for South Korean box-office admissions, the demon was quite literally a savage monster that came from the Han River in the middle of Seoul to feast on the metropolis.

In his latest film, "Mother," the monster is a single mother who goes to any lengths to prove that her mentally challenged 27-year-old son didn't murder a promiscuous teenage girl.

Bong, who was in Los Angeles recently for the Spirit Awards — "Mother" was nominated for best foreign language film — explained through a translator that he was intrigued to do a story about a mother-son relationship after watching "up close" the bond between his teenage son and his wife. He considers the bond between a mother and her son different than with her daughter because of the opposite gender. "It's a different kind of relationship (with a son) — it's a more special relationship."

And in "Mother" it borders on the sexual as mother and son share a bed. "There is some kind of (sexual) tension between them," notes the 40-year-old filmmaker.

"Mother" is anchored by the startling performance of Kim Hye-ja, a veteran actress who, says Bong, "is a national mother figure on television." Kim has starred for nearly two decades as the epitome of a loving mother on the Korean TV series "The Rustic Diary."

"I wrote the character for her," says Boon. "If she had said no, the movie would not have been made." Boon says that though Kim had played the perfect mother, he saw a dark side in her TV character, one that could become psychotic and crazy. "I thought she would want to play a part like this," says Boon. "When I first presented the story to her in 2004, the very first time I met her, she loved the story. She said I would love to do it."

She apparently relished the possessive, obsessive character. During one particularly violent moment, Boon recalls his leading lady telling him she wanted "more blood" for the scene. "She really enjoyed it," he says, laughing.

Still, he says, he didn't want to make the character a villain even when the audience learns that she tried to poison her son at age 5 by feeding him fertilizer. "Perhaps that incident may have caused his mental illness," Boon explains. "So that's why the mother feels more guilt for her son."

During preproduction, he watched Alfred Hitchcock's 1960 "Psycho," another poisonous relationship between a mother and son. "Even though the mother was dead in 'Psycho,' I thought what would have happened to the relationship if the mother was still alive."