The property the director looked for had to be a house of a very rich guy but with level and charisma. What they found was too small so they had to (temporarily) add the first floor (Anthony Zimmer's office). The filming crew had the villa only for two weeks.
When Tailandier looks at the IWC watch before going to sleep, it reads "00:05 am". But when the policeman is asked "When did they come back ?" he answers "01:15 am"
On the TGV when they meet and he comes back with tea and a tray, she folds the paper and it looks like it will unfold. Following shot, the paper is on the other side.