Sirius frowned at the book for several seconds longer than it deserved. How dare it take Remus's attention off of him for even a minute, really! But Remus had book it down now, and everything would be fine. Still, Sirius was totally prepared to lunge at the other boy if he reached for it again.
"Well," Sirius said, blinking innocently at Remus. "Since you ask! I thought that it would be fun to raid the kitchens and drop cupcakes on the firsties from the landing above the Defence classroom. It will be delightful, and you can't even say it's mean, cupcakes never hurt anyone and they can eat them after."