When Harry and the other two arrived at the Dormitory, they looked around but found no one.
Harry shouted in the Dormitory:
"Peter Pettigrew! Mr. Pettigrew!"
Wormtail, who was having a nightmare, had just escaped Black's pursuit and hidden in a Muggle home, intending to find something to eat.
Suddenly, he saw Harry Potter standing in the middle of the house, pointing a wand at him and calling out his name correctly. Terrified, he scurried all over the house...
George took the Marauder's Map and followed the ink dot, eventually reaching Ron's bed.
"Could this map have developed a problem because it's so old?"
Fred also said doubtfully:
"Surely not. We've used it for so long without any problems."
Harry frowned slightly and casually picked up the cage on the little bedside table...
George and Fred shouted at the same time:
"It moved!"
"It's alive!"
Harry looked at them in confusion.
"What moved?"
George and Fred looked at the cage in Harry's hand, then said to him:
"Take a couple of steps."
Harry had no idea why, but he still took two steps as they asked.
George and Fred tossed the Marauder's Map straight to Harry and snatched the cage from his hand.
"What do you think, George?"
"Take Scabbers out first and see whether it's a magical effect of the cage."
They knew Douglas had given Ron this cage. When Ron had shown it off, they had wanted to borrow it to study, but Ron had always refused.
As far as they were concerned, nothing Douglas gave away was simple, and now they had indeed found a clue.
Harry looked at the Marauder's Map in his hands and, sure enough, noticed something: Peter Pettigrew's ink dot now overlapped with the twins' dots.
He looked at the cage in shock.