I've watched Ratatouille several times now and have noticed a couple of mistakes.
The Disappearing jar
The first is when Linguini lets Remy out of the jar. Remy runs off and Linguini stands up. Remy looks back and the jar is at Linguini's feet. Then as Linguini turns to his bicycle the jar has vanished.
This one is more subtle. In the big chase scene as Skinner and Remy are jumping from boat to boat on the Seine. When Skinner does the screaming jump from the No Smoking Boat to the boat with the couple in love, we see most of his jump from the point of view of a camera on the deck on the Love Boat and he approaches it in a straight line toward the camera.
The mistake is that Skinner flight is directly toward the Love Boat in a straight line. The two boats are in motion relative to one another. Skinner would be moving at the speed of the boat he left and not the speed of the boat he is jumping onto. So from the Love Boat point of view he would be moving in a curve that would have had to start behind the man for him to end up grabbing the tablecloth.
Admittedly that might not have been as dramatic as what was put on screen but physics errors in movies are slightly bothersome to me.
This was something we ended up spending a lot of time on in my high school physics class. Several students couldn't figure out that the path of a falling object that was moving sideways was a curve. They kept saying it was a straight line. It turned out to be an optical illusion. The first experiment we tried was to have the teacher walk along and drop his keys. The optical illusion was that the keys were falling down beside his leg which looks like a straight line. Legs are straight and therefore the keys are falling in a straight line. After arguing about it a while I devised a plan to make it more obvious. I have the teacher stop and have the keys slide off his hand, then it was very obvious that the keys were traveling in a curve.