One scene that did not make the final cut showed that Abe was diabetic. The shot, which showed him taking time out of a conversation because he needed to give himself an insulin injection, was intended to establish that the circumstances of Abe's life have taught him to be careful and methodical.
The trivia items below may give away important plot points.
In the scene in which Abe-2 knocks out Abe-1 with nitrous oxide, the container he is holding is actually a rice cooker. Also, we see sleeping Abe's profile, but not standing Abe, because the latter was Shane Carruth standing in for David Sullivan.
Rules to Follow to Evade Causality Paradoxes or Generally Screwing Your Life Up: 1. Do not disturb the box after you exit it. You or your double is in it. 2. When re-experiencing time, stay away from your double until he/she has started his/her journey backwards. 3. Worry about yourself first. Now is the only moment that has to make sense. 4. Don't be too curious about your surroundings.