Banned in China: Pasternak's book was originally banned in the Soviet Union. A Dutch secret agent managed to get his hands on a Russian copy and he distributed it to his contacts at the CIA. They produced (technically pirated because an Italian publishing house held the original rights) thousands of copies of the original book and gave them to unsuspecting Soviet tourists at the 1958 World's Fair who smuggled them back to the USSR.
Enforced Method Acting: In an early scene, Komarovsky was supposed to kiss a shocked Lara. After noticing in rehearsals that Julie Christie was anticipating the scene and showing nervousness, Rod Steiger, with Lean's permission, decided, while kissing her, to not let her go and follow up that first kiss with a french kiss. It worked.
Throw It In: In another scene, after Lara slaps Komarovsky, he slaps her back with his glove. Komarovsky's response wasn't on the script. Rod Steiger later commented that "nobody slaps Komarovsky and gets away with it".