Sacha

Continuity mistake: When Grandpa exits the supermarket and lies on the floor his cap is on. A shot later it lies several centimeters away.

Sacha

Continuity mistake: When Grandpa is hanging the Xmas lights Sally's arms are crossed. Check her left fingers resting on her right elbow. They change positions in every shot.

Sacha

Revealing mistake: During the trampoline scene, there's a side shot of Grandpa jumping high. It is a very obvious stuntman for De Niro who looks nothing like him.

Sacha

Continuity mistake: When Peter reads his essay in class his folder keeps swapping between being open and closed, and parallel or perpendicular to the table.

Sacha

Revealing mistake: When De Niro/Grandpa falls down the roof and hangs on to the drain, he is replaced by an obvious stuntman with a wig and thinner build.

Sacha