“It’s his last chance he’s got until September,” Sirius whispered.
“But what’s he doing?” James whispered back.
The cloak shook from three shrugs.

He was there, all right. Pacing the hallway, right in front of the girl’s bathroom. Peter, as a rat, quietly snuck up to Snape, trying to hear or see what he was doing. Not knowing there was a rat there, Snape stepped on it. It squealed. Loudly!

They all jumped, spooked from the noise. Snape let out a muffled yell and ran off in the direction of the dungeons, and Peter scurried back towards the Gryffindor Tower.