 During the "hallway shot out" between Allan and Mad Dog, Tony Leung  (Allan) was cut in the eye by a shard of glass. It happens when the  two men are shooting each other from opposite sides of a set of  glass windows. If you pay attention, Leung suddenly covers his face  with his arm, an indication of when he was hit with the glass. Leung  was given a day off to get medical attention and returned to the set  to finish filming without problems.