Notice that The Fourth of July celebrates "independence". This is also the same day that Scamp get his independence from being a "house dog".
Angel's ears could be a physical metaphor her character: The folded one hides her true feelings away and the straighter one represents the facade she keeps up.
See Fridge Logic below regarding Scamp's age, but if we assume Angel is the same age as him, she'd be quite capable of having puppies by that time. Age taboos being nonexistent for dogs, it makes sense that Buster's so fixated on her. Doubles as Fridge Horror.
Tramp being part of Buster's gang (and Buster's friend) seems to clash with the first movie where he was a loner. But then, you recall what Tramp also told Lady in the first movie (that he has lots of families, but none of them own him). Like those families and restaurants, Buster's gang are another one of those "families" Tramp spoke of. He may hang out with them, but only for certain intervals at a time. Otherwise, they would've known that Tramp associates with humans who feed him.
Why does Scamp happily roll around in a puddle after he jumped over one earlier during "Junkyard Society Rag"? Because that was immediately after the lyric "where you can wet where you wanna wet"; he thought that puddle was piss.
Scamp's sisters initially roll their eyes at their brother's demeanor and even say that they don't want him to come home, when later on they worry about him as much as their parents do. The central theme of the movie is appreciating what you have, and here they are realizing how much they love him while he's gone. Talk about mirrored character development!
Despite it being just about a year since Tramp left the streets, he's become an eerily model house dog — obsessive about following rules and content to lay around on pillows all day. It seems odd that so much of the fire would have gone out of him so quickly, but remember that he and Lady have already had a decent sized litter of puppies. Jim Dear and Darling probably had him fixed.
Reggie, the borderline-monstrous stray we see as part of Scamp's initiation into the Junkyard pack and again during the final confrontation at the pound, only barks and snarls whereas all the other dog characters speak comprehensively. Reggie has been described as incredibly dangerous more than once, so that makes one wonder...is Reggie rabid?
He doesn't foam at the mouth or show signs of the disease, mind you (thankfully for Tramp, who could have been bitten during his fight with Reggie and caught the disease) but he may have something seriously wrong with him. He could have some severe, painful physical or mental disabilities, or be very poorly socialized by his owners, making him vicious and unpredictable. Barking rather than speaking coherently could be the canine equivalent of the slow, stilted speech a person deaf since birth or early childhood often produce.
