Continuity mistake: After Pongo spots Anita and Perdita walking towards the park, Pongo moves the time forward on the clock and he leaves the dial's hinged bezel open as he rushes to the door and barks, but when Roger checks the time on the clock the bezel is closed. (00:06:20)
Continuity mistake: When Sam Twist jumps from the train on the Forth Bridge, he lands in a puddle between the tracks, which are resting on sleepers on top of ballast - but when we see the train disappearing, there are no sleepers or ballast - the rails look like they're on concrete 'runners'. (00:55:00)
Continuity mistake: A spider web drawn by a girl near the fence disappears.