La Bocca della Verità

Mouth of Truth is a famous sculpted image of a human face in Rome, which is the most impressing stage in the movie "Roman Holiday". Sometimes I am wondering what is so called "lying or honest", is it a kind of "Uncertainty Principle"? Because it is impossible to seperate the current and past (memory inside brain) state. What the key point is that if we cannot grasp the fact holisticly, and what we say or determine is depend on what we know, thus the question of subjective and objective is quite vague.
However, it will not reduce any pleasure for me to enjoy this joyful movie. Recently I read a article about this scene that when Peck puts his hand into the "Mouth of Truth" (La Bocca della Verità), a stone face in Rome that legend says will bite your hand off if you tell a lie. In the film, when he pulls his hand out it is missing, causing Anya/Hepburn to scream. He then pops his hand out of his sleeve and laughs. Hepburn's shriek was not acting — Peck had decided to pull the gag he had once seen Red Skelton do, and had not told his co-star of it before. (by Wikipedia)