Continuity mistake: In the scene where the automaton stops drawing in Hugo's lair, in a close up there is a mysterious red spot on our right of Hugo's chin, but in the rest of the movie the spot is gone.
Continuity mistake: After Hugo and Isabelle see the picture of the moon printed on the book, their hands alternate between being on the book, to away from the book, between angles.
Continuity mistake: When the monkey-wrench falls, it lays on the middle of two tiles. When the angle changes, it lays on the center of a tile.
Continuity mistake: When Méliès shows up after the projection, the film suddenly disappears from the reel.
Continuity mistake: When the automaton signs the drawing, it makes a dot inches away to the right of the "L". When Hugo hands the drawing to the lady, the dot is a thick mark right over the "L".
Continuity mistake: After Frick gives the Dachshund, the Inspector looks at his watch and puts it in his pocket. When the angle changes, he is looking at his watch again and repeating all previous movements.
Continuity mistake: After Hugo's been saved by the inspector, he holds onto the automaton while being threatened by the cop. Méliès arrives and shouts, and for a brief moment the way Hugo holds the automaton completely changes.
Continuity mistake: The first time the doberman dog chases Hugo, it enters a hallway and skids. The passers-by behind differ between shots.
Continuity mistake: After the inspector saves Hugo, he yells at him "What were you thinking of?" Hugo's hair is moving wildly in one angle, still in the next angle, then wild, and finally back to still.
Continuity mistake: After Tabard shows the movie, he raises up twice.
Continuity mistake: While the inspector flirts with Lissette, she is standing sideways or straight, depending on the angle.
Continuity mistake: When Hugo bumps into Labisse and the books fall, their position changes between shots.
Continuity mistake: When the drawings fly all over the room, the ones on the box's lid appear / disappear randomly between shots.
Continuity mistake: When Hugo gives Mrs. Méliès the drawing, her hands change positions between the wide and the close-up angles.
Continuity mistake: Position and number of drawings on the bed in Mr Méliès' house differs between shots.
Continuity mistake: When Frick brings the Dachsund, the bag on the chair changes positions between shots.
Continuity mistake: When the automaton signs the drawing, the tip of the "G" is under a line circling the moon's face. When the angle changes, the "G" is covering part of the moon's face.
Continuity mistake: When Isabelle chases Hugo at the station and falls on the floor, her position is inconsistent between shots.
Continuity mistake: After the automaton stops writing for the first time, Hugo steps backwards and faces it with his head positioned straight. A frame later it's tilted to the left.
Continuity mistake: When Isabelle hands the key to Hugo, the length of the string attached to it decreases between the first and second shot.
Answer: He's not making it a point to chase down random children - he's like a security officer at an airport. It's his job to apprehend thieves and troublemakers and keep the station safe, and he only threatens to send children to the orphanage if they don't have parents for him to return them to. Also, it's implied once he finally apprehends Hugo that his particular harshness toward orphans (and most of his character flaws in general) is due to apparently having been one himself. He spells out the kinds of lessons he was forced to learn by growing up without a family, explaining how he became so cold, bitter, and antisocial.