Stu Richel played the husband of Jill Eikenberry in a scene with her former lover, played by Frank Langella. The Jill-Frank relationship was thought not to be "central to the spine of the story" and was dropped in the final cut.
When Ariel wears her t-shirt in close-up shots, her necklace switches back and forth between hanging outside the shirt and mostly hidden under the shirt.
In the scene where Leonard goes back to apartment after stroke, as he sits in the chair there's a boom mic shadow visible on the back wall. The scene then shifts to Lili Taylor, and when it returns the shadow has gone.
When Heather sits down to drink coffee with Leonard in the morning in his apartment, they each pour coffee in their cups. Yet, when they both sit down to talk and sip, there is no coffee in either of their cups.