On the train ride home discussing the apartment find, Fred's cigarette changes length from shot to shot.
When the boys are on the train, the whistle of a steam locomotive is heard on several occasions. The movie takes place in 1962 but the last steam locomotive on the New Haven Railroad was retired ten years earlier and, in any case, would not have been used from Connecticut to New York City.
During the little league game the runner on second base is three or four feet off the base while the pitcher is preparing to pitch. Little league rules require runners to have at least one foot on the base until after the pitch is thrown.
The boys suddenly decide to go check out the apartment as their train announces the 125th St. stop. But they're already 40 blocks north of East End Avenue.