Vacation movie directors reveal all on Chris Hemsworth's 'awkward' prosthetic penis fittings

Arriving in one scene in just his boxers he's packing a very significant package, one which is fitting for the man who plays Thor, but finding the right prosthetic was a challenging process...

The flick is the latest instalment in the long-running National Lampoon's Vacation series, starring Ed Helms as the son of Chevy Chase's character from the earlier films.

In an effort to boost some family bonding, a grown-up Rusty Griswold (Ed Helms) surprises his wife, Debbie (Christina Applegate), and their two sons, with a cross-country trip back to America's favorite family fun park: Walley World, as it will be closing forever.

At one point they shack up at Chris Hemsworth's house and Thor is quite proud of his rather large member.

Directors John Francis Daley and Jonathan Goldstein have revealed it was one of the "more surreal aspects" of preparing for the movie.

In an interview with Vulture he revealed that a stand-in was initially employed to try out penises of varying sizes, which was, according to Daley "the opposite of funny because you felt so bad for this poor stand-in".

Once Chris arrived, however, it became awkward again, "but in a funny way" as they whittled their options down to two sizes - an 8-inch and a 10-inch.

Of the 8-inch option, Daley reveals, "As big as it would seem, it did not look that big on him.  I think it was just because Chris is such a big, hulking dude."

Goldstein added, "He makes the normal-sized penis look small."