Up hidden details: the real people and places behind Pixar's Up

Up hidden details: how many balloons lift the house

A technical director estimated that 23 million balloons would really be needed to lift Carl's house. Docter cut the number down because that many balloons would look like tiny dots. The animators also made each balloon about twice Carl's size.

The final count was 10,297 balloons for the flying shots and 20,622 for the lift-off sequence, when the house first tears free of its foundations.

The real people behind Carl and Russell

Carl Fredricksen was designed to resemble Spencer Tracy in Guess Who's Coming to Dinner. Docter also drew on Walter Matthau, James Whitmore and the team's own grandparents. Ed Asner voiced him, and the writers gave him short lines with hard consonants to suit his voice.

Russell was modelled on Pixar storyboard artist Peter Sohn, whose sketch became the basis for the character. Jordan Nagai was cast at eight after Docter auditioned around 400 boys.

Where Paradise Falls comes from

In 2004 Docter and eleven other Pixar artists travelled to the tepuis of Venezuela, the flat-topped mountains in Canaima National Park. They reached Monte Roraima and climbed toward Angel Falls. Production designer Ralph Eggleston had shown Docter footage of the tepuis, which led to the setting.

The sheer cliffs and isolated plateaus in the film come from that trip, which explains why Paradise Falls feels like a lost world.

Charles Muntz and the dogs

The explorer Charles Muntz draws on aviators and adventurers including Howard Hughes and Errol Flynn, and Docter also cited Charles Lindbergh and Percy Fawcett.

Dug was created by Docter and Peterson for a project that never got made, and Peterson voices him. Dug's famous line, "I have just met you, and I love you," came from something a child said to Peterson when he worked as a camp counsellor in the 1980s. Alpha's squeaky voice grew from the idea of a record player stuck at the wrong speed.

Cameos and easter eggs

Some details are hidden in the cast list and the background.

• Dug appears earlier in Ratatouille, as a barking shadow that frightens Remy.
• Docter voices camp master Strauch and, uncredited, Kevin the bird.
• Docter's daughter Elie voices young Ellie in the opening.
• Kevin's movements were based partly on a Himalayan monal observed at the Sacramento Zoo.

The opening montage

The Married Life sequence that follows Carl and Ellie from wedding to her death runs without dialogue, carried by Michael Giacchino's score.

Watching again, notice how often Ellie's adventure book and the jar for Paradise Falls savings appear, small objects that carry the emotional weight of the whole film.

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