When Stone tells to Jim that Jack has changed while he is trying to get in the police station, the next shot is clearly not a direct continuation of the previous one because the positions of characters don't match.
At approximately 33.30 - 33.40, when old guy is yelling "Sam, is that you?" his pipe switches hands.
Cemetery is misspelled on map.
Icicles on the church wobble as if made of rubber just before Jack Frost arrives.
Numerous times throughout the film, snow is seen in the immediate vicinity, but in the distance, green grass is visible, as are trees with green leaves on them.
When Ryan is finishing up the snowman, there are clearly holes in the snowman to let the boy know where the buttons need to go.
When the boy is building the snowman (Jack Frost), it is evident that it's not snow by the movement of the man-made material.
Jake is clearly breathing after being killed.
(Before the girl gets killed by Jack in the tub ) Her boyfriend gets killed while she's taking her time blow drying her hair , after she's done blow drying her hair she gets in the tub & washes her hair.
Throughout the whole movie there's wind whistling, but there is never a visual indication of wind whatsoever.