These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
And also, this isn't the first time they talk and sing, they talked and sang sometimes in the original shorts, they just didn't do it all the time like in the movie, it's kinda strange how both of them became surprised when they realize the other one can talk, even tough both of them talked before, maybe it's Negative Continuity.
Yeah, but the voices don't match them in the show. I always figured it was one of those things none of the characters never noticed, like when Courage talked on Courage the Cowardly Dog.
The Scrappy: The movie itself is considered this by just about any fan of the traditional Tom and Jerry shorts. On a smaller scale, this also applies to just about every new character in it, especially Robyn Starling for leaving Tom and Jerry Out of Focus in what's supposed to be their movie.
Pugsy also gets a particularly bad rap for getting Tom and Jerry to sing about how they are best friends despite the latter two having been enemies since the beginning.
Squick: Aunt Figg and Mr. Lickboot look like they're about to kiss at the end of their Villain Song.