By Agnieszka Flak and Sarah Mills

VENICE (Reuters) - Director Amat Escalante uses a fantasy creature to explore the sometimes ambiguous relationship people have with sex in his film "La Region Salvaje" (The Untamed), which had its premiere at the Venice film festival on Monday.

The drama tells the story of Alejandra, a young mother of two, played by Ruth Ramos, whose boorish husband Angel, portrayed by Jesus Meza, has an affair with her gay brother, Fabian.

Their family triangle gets twisted further when the mysterious Veronica arrives on the scene and introduces Alejandra and Fabian to the octopus-like creature she is hooked on and challenges them to embrace their animal instincts.

Mexican Escalante said the creature was a better way than crude reality to embody the relationship people have with sex, seeking its basic pleasures but also looking down on it as something perverse.

"At the moment Mexico and many other parts in the world are in a situation where you want to look for another answer to things ... because reality is too much in a way right now," the 37-year-old director told Reuters in an interview.

"Once you've encountered this thing that is scary and grotesque, dirty, perhaps, it liberates you because maybe it is not what it seems, maybe it's not so scary, it's actually freeing, it makes you complete."

Ramos said doing nude scenes in front of so many people was not easy at first, but she also cherished the experience of learning how to move and match the special effects.

"The creature represents the subjectivity when talking about love and sex," she said. "Some find it crude and ugly ... while others like it."

Escalante, who received the Best Director prize in Cannes in 2013 for his drug war drama "Heli", said the idea for this movie - his fourth - was again inspired by issues in Mexico, but while others focus on crime and corruption, this one examines the macho culture and homophobia.

"The movie tells a story that's pretty melodramatic, but also a raw picture of reality ... the human reality between couples, family relations ... and explores the possible liberation of women in this society, and also men who cannot be what they really are," he said.

"I believe a lot of Mexicans will identify with this film."

The drama is one of 20 U.S. and international movies vying for the Golden Lion that will be awarded after days of screenings and red carpet glamour on Venice's Lido island.

The festival ends on Sept. 10.

(Reporting by Agnieszka Flak and Sarah Mills; Editing by Alison Williams)