During the lighting storm when Richard Tyler (Macaulay Culkin) is riding his bicycle. Immediately, after he exits through the tunnel, you can clearly see the lights used in the lightning gag reflected in his bike windshield.
During the scene in which the main characters first enter the cave/dragon's mouth, Adventure is overjoyed to find his sword. However, he never lost his sword in previous scenes. After Humpty Dumpty falls, you can see both Richard's glasses and Adventure's sword being carried by the pixies into the cave mouth.