Definitely a bad choice. Letting out a shout Sirius toppled over, chair and all. Falling back, he cracked his head against the nearby chair and the book smacked him right in the lip.
Ouch.
Squeezing his eyes shut, he barely noticed that Pince was upon them. "What are you two boys doing?!" the elderly woman insisted, seeing Sirius sprawled out ont he floor with -- "Is that one of the schools book I see laying haphazardly on the floor like that?" she asked, sounding quite menacing.