When Leonard is contemplating calling Allison, his dessert is on his side of the table. In the next shot, his nightcap is on his side of the table.
When Allison dumps the food onto Leonard's head, he goes back to his car and the amount of food keeps increasing and decreasing between shots. Look at the large leaf of Roamine lettuce disappear and reappear as Leonard Parker talks to Frayn.
In Leonard's first scene with Nurse Carvalho, the rice stuck to Leonard's face disappears and reappears between shots.
Leonard's armored Porsche has a roof-mounted tank-turret, a gun almost as big as the vehicle itself. Even if a sports car could be driven with such a weapon equipped, it would be all but impossible to fire said cannon accurately and without capsizing the Porsche.
When the frogs kill the agent outside of International Tuna, the lifts are seen to jump the car into the bay.