In two scenes of the animated movie, there's a character asking where they'll go and being told it's not a matter of "where" but "when". However, since the Time Machine goes through space as well as through time, both questions make sense.
At first, it might seem a little odd that all the historical figures at the end of the movie are standing up for Peabody with little incentive and declaring themselves to be dogs, too, but towards the beginning of the film, the "Beautiful Boy" montage showing Sherman's childhood makes it clear that Peabody got to know and befriend many famous historical figures, possibly all of the ones who ended up being transported through the wormhole. They're not just supporting Peabody because it's right, most of them are probably doing it because he's their friend.
At the very least, the movie was not the first time Peabody met Leonardo da Vinci. The movie implies that Peabody and Sherman visit Renaissance Italy on a regular basis.
In the scene where Peabody, posing as Anubis, threatens the Egyptians that if the marriage is sealed, there will be plagues unleashed on the city. One random guy in the crowd says "Oh again with the plagues, why did I ever move to Egypt?". This line has a double meaning; Not only had Ancient Egypt been known for welcoming immigrants of every background with great hospitality, but it is also a funny Shout-Out to one of DreamWorks's earlier films, which involves plagues hitting Egypt in one scene.
The gag of Benjamin Franklin pulling all the ladies to him is actually accurate to a degree: he was quite a ladies' man no matter how old and fat he got. The difference is in the kind of ladies he liked.
The school Sherman goes to is the "Susan B. Anthony" school. This is actually a perfect school choice for Mr. Peabody to send Sherman. Ms. Anthony was the first woman to vote and got arrested for it; Mr. Peabody was the first dog to adopt to a boy and faced some prejudice (namely from Ms. Grunion) because of it.
Mr. Peabody insisting that Sherman not call him Dad could be seen as his emotional detachment/ultra logical way of seeing the world, but there could be a subtle bit of brilliance in there. When parents adopt, sometimes they don't insist that they be called Dad so as not to diminish the former parents in the eyes of the child. Thus, Mr. Peabody could be preparing for Sherman's later crisis of identity when he begins asking more about who his biological parents were.
Why on earth is the WABAC a red spheroid? It doesn't seem to be based on anything, though Peabody seems close to the Doctor from Doctor Who. But a red, clearly futuristic space-apple is almost the exact opposite of a mundane-looking blue police box - oh.
In the "Beautiful Boy" montage, it's shown Mr Peabody writing a story (for Sherman) and signing it under William Shakespeare. There has been debate over whether or not Shakespeare actually wrote any of his plays at all.
It's not that surprising that Agamemnon would put a child in danger to fight the Trojans; he was willing to murder his own daughter, Iphigenia, in order to actually leave to go to war (the wind refused to blow unless he did so).
The only prehistoric era Mr. Peabody and Sherman appear to have visited at one point was the Ice Age, and never any geologic era further back, not even the Mesozoic Era. All of the time periods visited occurred during human history (as humans have just evolved during the ice age), and back then, people didn't know what dinosaurs were until the 1800s, and evolvingscience would've made historical depictions of dinosaurs inaccurate to today's depictions.
Stuff from Peabody and Sherman's adventures from before the film start dropping through the wormhole, including the RMS Titanic. What if Peabody and Sherman visited say, Trinity, New Mexico for the world's first nuclear test? They may have come within seconds of vaporizing downtown New York City.
Or, what if Peabody and Sherman visited the Mesozoic era, specifically the Cretaceous period, and that asteroid came down?
And also, the RMS Titanic is shown falling out from the portal down to the city below. And when you remember that there are more than 2,000 people on the ship, as well as possibly even more on the streets...? There Is No Kill Like Overkill indeed.
Sherman is 7 (and a half). Mr. Peabody is older than him (by a few years, at least). Sherman could end up an orphan before he's eighteen. Dogs don't live that long.
We should just hope Mr. Peabody's thought of that and is trying to fix it.
It's obvious Peabody is not a normal dog, so he may actually have a longer life span.
That's right. It's safe to say that he will last much longer. Just check out when Zumba became a success [1]. Peabody must be at last 10-15 years by 2014 and there are no signs of old age!
Someone left a baby in a cardboard box in an alleyway. In the rain. It is far too easy to imagine what might have happened if Mr. Peabody didn't come along...
Paul and Penny are hostile and mean to Mr. Peabody and Sherman from the outset of the dinner party, despite the fact that, as was revealed during the black hole scene, they knew all along that Ms. Grunion was planning to separate Sherman from Mr. Peabody.
The Beautiful Boy flashback sequence features John Lennon's song with certain parts edited out: The coda where Lennon dedicated the song to his son, Sean (Darling, darling, darling, darling Sean.), for the obvious reason that's not the name of the boy in the film. They also edited out a part the song's bridge which included the lyrics:
I can hardy wait, to see you come of age, but I guess we'll both just have to be patient.
The song was released on the Double Fantasy album a mere three weeks before John Lennon was murdered when Sean was only five years old. It's heartbreaking to realize Lennon never got to do what the lyrics say and see Sean grow up; it would've ruined the heartwarming tone of the scene if it hadn't been edited out.
After biting her, Ms. Grunion implies that she's going to have Mr. Peabody put down. Even though Mr. Peabody is as sapient as a human being (and a genius), it seems he'll still be killed for actions that would be unjust cause for killing a human, simply because he's a dog.
. Peabody must be at last 10-15 years by 2014 and there are no signs of old age!