The dragon - for it is indeed a dragon, though not any species Ron has ever heard of - pins the massive werewolf simply by lying down. The 'wolf struggles, scratching and biting at the dragon. It doesn't do a thing.
Pettigrew somehow managed to dodge and pull ron out of the way while he was at it. The little man eyes the dragon warily for a moment then turns to Black. "Right. So, how shall we do this?"
Black cocks his head, thinking. After a moment he says, "I think the belly crawler routine might be our best bet."
Pettigrew grimaces. "Gods I hate that one. It's humiliating."
A look at Harry and Hermione show them to be just as clueless. Ron is just decide to speak up when Pettigrew turns back to him.
"Sorry about this. No hard feelings, yeah?"
Ron sees then that Pettigrew has Lupin's wand and then he knows no more.
AN: For some of these, it's a guessing game. Don't worry, I always know who the character is and I'm happy to tell you if a guess is hot or cold.