Paul Dano revealed in an interview that he wanted to be in the movie after hearing a one-sentence synopsis from directors Daniel Kwan and Daniel Scheinert. Specifically, the directors told Dano they wanted to make a movie where "the first fart makes you laugh and the last fart makes you cry."
Daniel Radcliffe promoted the movie by touring Los Angeles and New York City with a Manny doll as his companion, attending interviews, fan conventions and even roller coasters next to him.
A fake version of Manny was made to be used in most of the film, but Daniel Radcliffe insisted on being in every shot. The dummy was only used in a few shots where the stunts were too dangerous for Radcliffe, but Radcliffe would still throw or toss the dummy.
Daniel Radcliffe has stated that this is his favorite film of his.
Paul Dano's character is named "Hank Thompson" which is a reference to Tom Hanks who starred in Cast Away - Verschollen (2000) that had the same deserted island theme.