Harry Potter needed the Marauder's Map to get into Hogsmeade, so Fred and George gave it to him because they now knew every location by heart. They advised what secret passageways he should use, because a few had been found by Filch and a few had caved in or been difficult to get to.
George dropped another Dungbomb, while Fred stole the map from the drawer. They had to experiment with it in order to learn how to get it to work, but it gave them clues, "flickering into life here and there" when they came close to the activating phrase, until finally they got it exactly.
Perhaps no students (even including Harry Potter, Ron Weasley, Hermione Granger and Tom Riddle) have ever explored the castle and grounds of Hogwarts as thoroughly and illicitly as the four creators and contributors to the Marauder's Map: James Potter, Sirius Black, Remus Lupin and Peter Pettigrew.
Fred and George never noticed Pettigrew on the Marauder's Map because they didn't know who he was. Even if they had recognized his name, they would have assumed he was just a student with the same last name.
Snape did not recognize the Marauder's Map because he has never seen the map before. The marauders would never show it to him and he did not know about it to recognize it. There is no scenario which would lead the Marauder's to show their map to someone they did not like - Snape.
Argus FilchThis artefact proved quite useful to the foursome (commonly termed "the Marauders") through the years, until it was confiscated by Argus Filch.
Black and Lupin explain the reason behind the group's nicknames. They adopted the nicknames Moony (Remus Lupin), Wormtail (Peter Pettigrew), Padfoot (Sirius Black), and Prongs (James Potter), the nicknames were derived from their altered shapes: a werewolf, a rat, a black dog, and a stag, respectively.
This allowed them to safely accompany Remus during his transformations and keep him under control. Sirius's form took the shape of a huge black dog (not unlike the Grim), from which his nickname "Padfoot" was derived. James would become a stag (Prongs) and Peter would become a rat (Wormtail).
This was not long before the first film came out - maybe even after it did - and even if it was before, by that point Warners may already have cast Alan Rickman, who was a lovely actor and a lovely person but really 20+ years too old for Snape, who is only 31 when we first meet him.
1988Portrayed by. We're getting no help from Flash Gordon here." Peter Jason Quill is a Celestial-Human hybrid who was abducted from Earth in 1988 by the Yondu Ravager Clan, eventually building a reputation as the notorious intergalactic outlaw Star-Lord.