When the Messenger Boy meets with White Vincent at the top of the stairs, he begins writing on a note pad. As the shot changes, he switches from right-handed to left and back again. Also, how he grips the pen changes as well.
Among the stock shots that establish that some of the action takes place in Paris, the image from the hotel is actually the front from the Czech Ministry of Regional Development in Prague, a building of Baroque style, carrying a Czech flag.