As far as mysterious happenings in Hogwarts go The Case Of The Disappearing Defence Teacher isn't that big of a deal. Harry disagrees, which is fair enough with their track record, but Ron thinks that in this case he probably really is sick.
Most of the time Lupin disappears for a day and looks like death warmed up the next time anyone sees him but this time half the students in Hogsmeade had seen him out and about, Ron included.
Alongside Harry's 'All of our Defence Against the Dark Arts teachers want me dead' theory is the more prevailing theory amongst the students that Sirius Black has kidnapped their professor.
Some students are going on about The Curse, whatever that is. Snape is looking rather triumphant; as though he knew all along that this would happen. Or more likely, Ron supposes, pleased that he'll have more chances to traumatize everyone in his cover lessons.
"Ah, Ronald." A slightly out of breath voice accosts him, and he give a small (and completely manly) yelp of surprise, turning to see the very subject of his thoughts behind him looking slightly manic.
"Where've you been sir?"
Harry and Hermione are too far ahead of him for Ron to sure but he's almost certain that he hears Hermione tut at his lack of finesse.
Lupin only smiles in reply. "I'm afraid I can't tell you that. I was wondering if you happened to have your pet rat on you?"
"Scabbers?" Ron wrinkles his forehead in confusion, but obligingly reaches into his robes pocket. "Yeah he's right he-OW!"
Scabbers bites hard on Ron's finger and drops out of his hand to scurry quickly down the corridor and away from them; luckily he runs in the direction of Harry and Hermione, and Harry is able to use his finely-honed seeking skills to grab the rat and firmly grip him from the behind.
"Here." Harry says, jogging forward and passing Scabbers back to Ron, "Merlin he's nervous."
Professor Lupin snatches Scabbers before Ron can reclaim his rat, and both boys turn to look at him in surprise.
"Are you alright Professor?" Harry says suspiciously.