Continuity
When the little girl gives half her sandwich to the little boy on the dock, he takes the other half, and hands the first one back to her. As he hands it over, there is a bite missing in the middle. When she goes to eat it, it is whole.
When Chris is about to jump off the cliff to the purple tree, he takes off his tie. When he and Albert are at the tree, the tie is back. It leaves again when the tree is melting.
When Chris causes the pen to write "I still exist," the insert shot of her examining the writing is a different written page.
When the bird drops paint on Chris, the shot from above shows it hitting the top of his head and his shoulder. When the angle changes, the paint is on the side of his face and his shoulder, with none on top of his head.
At the end of the movie when Chris and Annie are reunited in "heaven", Annie has nicely tweezed eyebrows but then in the next shot she has thick eye brows.
During the flashback when Chris is talking to his son in the rain, standing next to a tree, Ian's hair switches between being plastered across his forehead to just one side between several shots.
When Christy and Ann are in the park watching the clouds, the leaves in her hair disappear and reappear between shots.
When Annie and Chris are reunited in Heaven, as they are facing each other talking, Annie's hair is in her face. The shot briefly changes, and when it returns her hair is fixed.
In the original presentation of the car crash scene near the beginning of the movie, the windshield wipers are moving at different speeds and the sky is drastically different between shots.
When the car is launched into the air and is about to slam into Chris, it shows him bracing for impact. In the next shot he is not there when the car slams into the other car.
In the arrival to the 'Library', the camera makes a long-shot where it appears a great hall with a lake like ground, without corridors nor bookshelves. When seconds after Chris and Albert fly from the boat to the Tracker this one is reading a book between two bookshelves, floating in a corridor (located in the middle of the great hall) that wasn't there before.
Crew or equipment visible
When Chris is entering the tunnel to help out with the accident, the shadow of the camera on a crane can be seen on the wall.
Revealing mistakes
As the supposedly invisible Chris walks down the aisle of his own funeral, one of the extras can be seen watching him.