When Ethan (Kevin Costner) enters a tattoo parlor, one can see the nude back of a girl with a very mexican "Lady of Guadalupe/Holy Death" tattoo. This mystery girl is also seen tattooing Mr. Jang (Choi Min-sik) in the movie Lucy (2014). Both films were written by Luc Besson. The tattoed model is uncredited in both films.
When Ethan Renner (Kevin Costner) tries to get the French police to remove the family of immigrant squatters from his little-used Paris apartment, they tell him he must wait until April 13, when winter ends. And when he threatens to do it himself, they tell him he'll get arrested. There is, in fact, a law in France that protects squatters who occupy a residence during winter for more than two days. The owner can't remove them except by filing a lawsuit.
The term "3 Days to Kill" is coined by Zooey (Hailee Steinfeld) during the breakfast cooking scene when telling her father how much time they have to spend together.
The car Vivi Delay (Amber Heard) picks Ethan Renner (Kevin Costner) up in is a Peugeot RCZ and retails for around $36,000. According to Peugeot, actress Heard liked the car so much she wanted to perform her own stunts.
The check for $150,000 that Ethan (Kevin Costner) receives for his services is curiously dated, November 22, 2013, the 50th anniversary of John F. Kennedy's assassination, a crime Costner (as D.A. Jim Garrison) investigated in JFK (1991).