Obviously different "Jaime + Steve" tree-carving used in the "clasping hands for a whole new start" shot --- different bark/exposed-wood colors, writing style, the size/positioning of the surrounding carved initials on the tree trunk, etc.
If Jaime had actually hit the tennis ball hard enough to make it crush itself from its ricochet off the clay court and then still have enough force left to tear a hole through the heavy chain-link fence, Jaime's tennis racket would surely have had its strings ripped out by the ball's contact, since no tennis racket (especially in the 70s, before Kevlar was widely used) would ever be tougher than a steel fence's heavy-mesh fabric.
If the brake line was broken in Jaime's car, the brake pedal would have had no "stiffness" in its travel, the way it does when she steps on the brake to try to stop the car after the detonator goes off; the pedal would have just sunk easily to the floor, as it does when a mechanic and his assistant are bleeding a vehicle's brake lines prior to adding more fluid.
Jaime would not have been able to bionically tear the phone book in half just by using her hands, since just her one hand/arm is bionic. She would have had to use her knee or foot as part of her grip on the book.
Jaime asks the old lady if she can say something "just between you and I?". The correct grammar is: "just between you and me", because that is the accusative case. It can be replaced by "just between us" (you and me) but not by "between we" (you and I). "You and I" is the nominative case, as in the subject: the words often start a sentence, rarely end it.
All the carvings on the tree (Steve's and other lovers' messages) are all the same color; obviously they were all carved at the same time, rather than having been added one at a time over the course of weeks or months, the way they realistically would have been by successive romantic couples who had happened to stroll through that part of the expansive park and seen that previous lovers had made their marks on the tree, and so they'd decided to do the same thing themselves.
When Jaime is opening the can of tuna the lid is obviously made from aluminum foil. When she removes it one can also see the lid has been changed to the original with a set of numbers on top that were not on the foil.
When Jaime is speaking with Steve on the phone, there is a dial tone sound effect right after she says "goodbye", even though she has not hung up the phone and the very next shot shows that neither has Steve.
Jaime claims that she doesn't remember ever going skydiving, yet she had made a dive with Steve just a short while before, to try to blow up Carleton Harris's factory. This had happened long after her bionics-rejection traumas that had mostly erased her "previous life" memory, so this event is something that she would have remembered, since her more "recent" memory capability is still working okay.
The medic running the slide projector shuts it off completely after showing Jaime the slides; he doesn't leave the cooling fan running for a while, the way any experienced projectionist knows to do.
Jaime is obviously very interested in the scrapbook of Steve's past, yet when she first opens the book, she initially turns over a sizable sheaf of pages instead of just the first one, so that she totally misses seeing the first several leaves. She does this same multiple-page-turning sometime later, also, just before the page of her and Steve's engagement announcement.