Harry wrote back to Sirius saying that he would be beside the common room fire at the time Sirius had suggested, and he and Hermione spent a long time going over plans for forcing any stragglers out of the common room on the night in question. If the worst came to the worst, they were going to drop a bag of Dungbombs, but they hoped they wouldn't have to resort to that--Filch would skin them alive.
Dungbombs were magical stinkbombs that aided the mischievous in creating odorous diversions.
When thrown, one of these magical stinkbombs gives off a putrid odor, which is handy for creating a diversion.
Tags: banned distractions diversions pranks smells smelly/smells