A defibrillator delivers one instantaneous jolt, not an extended current. Once the paddles discharge through a conductor (like the human body), they are no longer electrified until he machine is activated again and can build up a charge.
In the first scene with Lonnie in his house, he says he was in the Air Force. In the last scene, he is flying and steps out of a helicopter. He clearly wearing a US Navy flight suit. In the U.S. Air Force, squadron patches go on the left shoulder while the Air Combat Command patch (which all USAF pilots wear) goes on the right chest. On Lonnie's flight suit, his squadron patch on his right chest, and it is for VFA-41 "Black Aces". The Black Aces are a U.S. Navy Fighter Strike Squadron utilizing the F/A-18F Super Hornet fighter jet. The Black Aces were commissioned in 1945 and have never had helicopters assigned to their squadron.
At the end of the movie, after Dr. P drops the defibrillator paddles on Roger, he is seen shaking like he has been shocked even though only one paddle is on him and the other can be seen on the ground. The circuit would be open the second the other paddle is not touching his body.
Roger goes to visit Lonnie in Peekskill, a suburb about an hour away from Manhattan. From Grand Central Terminal Roger would take the Hudson Line to get to Peekskill. As of 2008 the Hudson Line still uses the older trains with red and blue chairs. The train Roger is on has blue and green chairs, which are seen on other lines. Basically the train Roger is seen on would not have taken him to Peekskill.
Incorrectly regarded as an error: The first time Roger and Dr. P are in the museum, there are two elephants in the background. The next time there appears to be only one in the final shot. This is caused by the shift in camera angle. In fact, the head of the elephant on the left is hidden by the stuffed lion. The body of the elephant is still seen, but looks like a large boulder.