The Day of the Jackal (1973)

Plot hole: When the French conclude - incorrectly - that Charles Calthrop is the Jackal, they contact the British authorities and obtain his file photograph from the passport office. The photograph is of Edward Fox in character as the Jackal - but it shouldn't be! The Jackal and Calthrop have no connection. The Jackal never used his identity and did not apply for a false passport in his name. The photo should have been of Edward Hardwicke in character as Charles Calthrop, who appears in the closing minutes of the film. The two actors do not look anything like each other.

Caron: You know, sir, what they'll do to you if you don't catch this man in time.
Lebel: I've been given a job to do, so we'll just have to do it.
Caron: But no crime has been committed yet, so where are we supposed to start looking for the criminal?
Lebel: We start by recognizing that, after De Gaulle, we are the two most powerful people in France.

Trivia: The Jackal demands $500,000 (US) to assassinate De Gaulle, which seems like a modest amount for such a dangerous job. However, when you take inflation into account that's the equivalent in 2024 money of over $5m. No wonder his putative employers are surprised.

Question: Before the Jackal makes an impression of the Paris apartment key, he deliberately rubs the key against his chin. Why?