"Though Wyler generally liked to stick to the script, the location shooting allowed a great deal of room for spontaneity in order to take advantage of any wonderful new discoveries he happened to come across. “Filming in Rome in those days was marvelous,” said Wyler. “There were practically no automobiles, only Vespas. For every scene I could have had six locations, and each one was better than the other.” When he wasn’t making use of the beautiful Roman outdoors, Wyler used the newly renovated Cinecitta studios to shoot interiors.

A good example of this spontaneity while shooting is the film’s famous scene that takes place at the Boca Della Verita (Mouth of Truth), an ancient stone monument at the entrance of an old church. The legend of it said that if a liar put his hand inside the mouth, he would lose the hand. A truthful person, however, would have nothing to fear. Wyler said that he had gone sightseeing one day with his daughters to the monument and played a joke on them, sticking his hand into the mouth and pulling it out with his hand hidden under his sleeve. The joke terrified and delighted them. “So I thought there must be a place for this in the picture,” said Wyler. “Especially since it’s a story of two people who lie to each other.”

Excerpt from TCM located HERE.