In the beginning sequence, the ice cream truck reads (on the back doors): "Watch Out For Children." Later in the movie, we see that Gregory has painted over the word "For" so that it now says: "Watch Out Children." But, at times, the word "FOR" is mysteriously back on the van, sometimes from one shot to the next.
When the Ice Cream Man's store is being trashed by the police, you see Ice Cream Man wading around in the spilled ice cream. Ice cream gets all over his shoes and his pant legs. Later on when he is outside, there is no ice cream glop on his shoes, and his pants are clean.
Heather's orange cream cycle changes in different shots.
When the Rocketeers first go to the park, Johnny goes and stands near the swing on the left of Small Paul and then repeatedly disappears and reappears between shots.
The character of Tuna is supposedly obese and out-of-shape, however, the facial features of the actor playing him are clearly those of someone who is not obese and it's obvious that he is wearing padding under his clothing in order to appear larger.