Emma Thompson almost made an accidental uncredited cameo in this movie while visiting friend Liam Neeson on the set. Thompson, who'd been filming Nanny McPhee Returns (2010) in an adjacent studio, went to visit Neeson during a break, just as Neeson was about to shoot a scene with Ralph Fiennes and Danny Huston. Unable to exit the set fast enough as the cameras began to roll, Thompson, in her clumsy Nanny McPhee costume, had to hide behind Huston's throne during the take so she would not be picked up by the cameras.
The word Kraken (sea monster) is Norwegian/Swedish, not Greek. Early script drafts considered changing it to its Hebrew counterpart Leviathan (famous from the Bible hymn of Job 41). It was changed back to Kraken as a tribute to the original Clash of the Titans (1981) tagline "Release the Kraken!" Surprisingly, the creature's Greek name, Cetus, was never considered.
The language of Djinn is actually Arabic.
Sam Worthington's sandals are Nike Trainers with toes painted on them. He didn't wear sandals because he needed shoes to perform the stunts well.
In Greek mythology, Io is Perseus' great-great-great-great-great-great-great-grandmother, and an old flame of his father Zeus.