For Robert Pattinson, it was the elephant that sealed the deal.

The Twilight star, 24, was on the fence about taking the role of Jacob, a veterinary student who joins a traveling circus in the upcoming Depression-era romantic drama Water for Elephants – until the actor met Tai, his 42-year-old, nearly 9000-lb. costar.

"Rob was non-committal until he saw the elephant," recalls the film's animal coordinator Paul 'Sled' Reynolds. "After he met Tai, he knew he wanted to do this movie. He absolutely adored that elephant."

PEOPLE has a first look at some of the film's rich images – and Pattinson's near smooch with Tai.

The adaptation of Sara Gruen's bestselling novel, which arrives in theaters on April 22, tells the story of a love triangle that develops between Jacob, Reese Witherspoon's Marlena, who is the show's bottle-blonde star performer, and her husband August, the circus's abusive ringleader, played by Oscar-winning Inglourious Basterds star Christoph Waltz.

Chemistry Lesson

While it was important to the filmmakers that Pattinson bond with Tai, their chief concern was making sure sparks flew between him and Witherspoon, 34.

"I saw early on that those two had a real on-screen chemistry," the film's director Francis Lawrence (I Am Legend) tells PEOPLE. "There was just this thing that happens between the two of them when they are together as those two characters that was very exciting."

FIRST LOOK: Robert Pattinson & Reese Witherspoon in Water for Elephants| Movie News, Reese Witherspoon, Robert Pattinson

Robert Pattinson and Tai

Twentieth Century FOX

A Sensitive Guy

Lawrence became convinced that Pattinson could pull off the challenging role of Jacob shortly after a meeting with the British heartthrob to discuss the part.

"When I sat down with Rob, I found that despite his success, there was a real sense of humility with him," says Lawrence. "I found that he was kind of uncomfortable in his own skin, and maybe even uncomfortable with everything that was happening to him. Rob is a very sensitive guy who very much loves animals."

Adds Lawrence, "I found that, wow, this guy kind of already is Jacob."

People via 500daysofRK