Jake Gyllenhaal has hailed Robert Downey Jr. as a "genius" and compares working with the actor to playing jazz. The pair worked together on new movie Zodiac - a film based on a true story - in which Gyllenhaal plays Robert Graysmith, a cartoonist at the San Francisco Chronicle, who embarks on a quest to identify a 1960s serial killer. And the Brokeback Mountain star was constantly in awe of Downey Jr.'s passion for his art. Speaking at the Cannes Film Festival in France yesterday (17May07), he said, "A very good, typical actor has about 25 really interesting choices and ideas within a minute. And then there's Robert Downey Jr. who has, I would say, 500 to 750 ideas. "Some people would call that madness. I would call that genius. "You're running around an actor and then they're chasing you, all of a sudden - that's a wonderful thing where rhythms are all over the place, it's like playing jazz with somebody."