Blithering Mc Gonagall

The Marauders Map scene in POA: Verbal Fencing Between Snape and Lupin

The fun of having Harry-centric third person POV is rereading the books and seeing things with context of what we know. The particular scene I am pulling up is classic veiled fencing between adults, while Harry remains clueless.

Snape discovers that Harry has been going to Hogsmeade illegally (thereby making his job of protecting him harder - as he says: "Everyone from the Minister of Magic downward has been trying to keep famous Harry Potter safe from Sirius Black. But famous Harry Potter is a law unto himself. Let the ordinary people worry about his safety! Famous Harry Potter goes where he wants to, with no thought for the consequences")

He gets him to empty his pockets and sees the parchment we know as Marauders map. Once he tries to get the parchment to reveal it's secrets, the map insults Snape.

As though an invisible hand were writing upon it, words appeared on the smooth surface of the map.

"Mr Moony presents his compliments to Professor Snape, and begs him to keep his abnormally large nose out of other people's business. "

Snape froze.

Given that he reacts to the first insult, I am inclined to think he recognised the names. Since Marauders were openly calling each other by their nicknames in Pensieve memory, it's not a stretch to assume he knows. And then he calls Remus, supposedly on the pretense that since the parchment is full of Dark Magic, and Lupin is the Dark Magic expert as DADA teacher, he would recognize it. But the readers know that the actual Dark Magic expert is Snape, not Lupin, so it is clearly an interrogation that was borne from him recognizing the names.

"You called, Severus?" said Lupin mildly.

"I certainly did," said Snape, his face contorted with fury as he strode back to his desk. "I have just asked Potter to empty his pockets. He was carrying this. "

Snape pointed at the parchment, on which the words of Messrs. Moony, Wormtail, Padfoot, and Prongs were still shining. An odd, closed expression appeared on Lupin's face.

"Well?" said Snape.

Lupin continued to stare at the map. Harry had the impression that Lupin was doing some very quick thinking.

"Well?" said Snape again. "This parchment is plainly full of Dark Magic. This is supposed to be your area of expertise, Lupin. Where do you imagine Potter got such a thing?"

Snape tries to see if the map gets a reaction out of Lupin, but Lupin immediately has defaulted to a "closed expression". To prod Lupin further, Snape makes a veiled accusation that Lupin gave Harry the map to lure Harry out of school and into possible danger. As we know from end of the book, Snape believes that Lupin and Sirius are working together: "I have been telling Headmaster again and again that you have been helping your old friend into the castle, and now here's proof". We see him relaying these doubts to Dumbledore in the chapter after Sirius's Halloween break-in - that he thinks it's impossible to get inside without help, a conversation Dumbledore shuts down in front of Percy Weasley.

Thereby, in this scene, he is implying that Remus is working with Sirius to lure Harry out of a safe space by handing him their old invention as means. A fact Remus immediately cottons to. He confirms this when Harry asks him after the scene:

"Why did Snape think I'd got it from the manufacturers?"

"Because. . . " Lupin hesitated, "because these mapmakers would have wanted to lure you out of school. They'd think it extremely entertaining. "

To deflect this accusation as well as to cover for Harry in front of Snape (who Remus has a poor opinion of as an authority figure - as established in Boggart scene), Remus goes for a feigned Deer in Headlights approach:

"Full of Dark Magic?" he repeated mildly. "Do you really think so, Severus? It looks to me as though it is merely a piece of parchment that insults anybody who reads it. Childish, but surely not dangerous? I imagine Harry got it from a joke shop --"

Snape, angry, presses the accusation further:

"Indeed?" said Snape. His jaw had gone rigid with anger. "You think a joke shop could supply him with such a thing? You don't think it more likely that he got it directly from the manufacturers?"

Remus goes so hard into deflection that it is almost comical:

"You mean, by Mr. Wormtail or one of these people?" he said. "Harry, do you know any of these men?"

"No," said Harry quickly.

"You see, Severus?" said Lupin, turning back to Snape. "It looks like a Zonko product to me --"

Ron comes in at this point and confirms Remus' story.

And then he accidentally slips up:

"Well!" said Lupin, clapping his hands together and looking around cheerfully. "That seems to clear that up! Severus, I'll take this back, shall I?" He folded the map and tucked it inside his robes. "Harry, Ron, come with me, I need a word about my vampire essay -- excuse us, Severus --"

After pretending the entire scene that he knows of nothing of the map and it's probably a Zonko product, Remus has a Freudian slip of: "I'll take this back, shall I?"

Snape is not having a good time in most HP books, but POA is especially a book where he is having a No Good Very Bad days.

For more reading on traits touched upon here, read this meta by u/metametatron4 [Remus Lupin: Canon vs Fanon]

Another amazing and thought provoking meta from the brilliant @ashesandhackles

A must read