Convicted

Harry might be in a world of trouble. All his own fault, of course.
"Explain yourself." Snape ordered.
"I decided to practice the spell that reveals an animagus on Ron's rat?"
"How did you know it was Pettigrew?"
"His finger. When he was allegedly blown to bits, that's the only part of him they could find."
Ron looked almost humorous, "He was naked and the thing you focused on was his finger?"
"Yes, I'm very observant."
OR: Harry does a plot point.