Arnold's phone number is 555-123, but all phone numbers in the USA have seven digits.
It's unknown if Harold gets grounded for refusing to give Cupcake back to his owner.
When Arnold tells how much the kitten might miss his owner, Harold's hat turns blue.
In Arnold's room, the flyer says "spot", but when Harold sees it, it says "spots".
The front door to Harold's house has wooden boards nailed to it to keep people out. How did he get back inside? It is possible he went through the window, as Arnold did so easily to try and reason with him.
When Arnold is talking to Harold in his room, one of the sandbags said Samd or possibly sand with a backwards "N"
In this episode, the doorbell at Harold's house is a buzzer. But in previous and subsequent episodes, it's a traditional chiming doorbell.
Rhonda, Gerald, and even Sid (who is one of Harold's closest friends alongside Stinky) refuse to let Harold play with them even though in other episodes their friends with him even if they don't always get along. This episode could either have happened before those episodes or more likely they were just mad at him at that moment but later made amends as hinted in the end of the episode.
