Such was the physicality of Saoirse Ronan's role, her combat tactics called for four-hour days of intense training under Dan Inosanto (a Bruce Lee protégé) over a two month period at his Los Angeles, California gym.
Director Joe Wright bleached Saoirse Ronan's eyebrows to try and mimic the appearance of a white wolf.
Erik Heller's arrival in Germany and fight in a passage underground below the ZOB bus station was done in one long take. It took less than ten attempts to get it right.
Saoirse Ronan: [underground] Hanna escapes from an underground base. In City of Ember (2008), Ronan's character lived in an underground world. She also starred in Lost River (2014), about a city under a lake.