one day, frustrated at sirius’s distracting roughhousing and lack of consideration, remus lupin turns in his seat and shouts, “i told you to be quiet because some of us have exams tomorrow! i’m dead serious about this, so if you could please take your rioting elsewhere i’d appreciate it!”
to remus’s dismay, sirius merely snickers, “dead sirius, huh? poor moony, struggling to study for exams he’s already prepared for,” and proceeds to repeat “dead sirius” exaggeratedly to the gryffindor common room at large. after a little while sulking over his arithmancy, remus good-naturedly gives in to the inevitable as usual, joining in the common room fun.
from then on, remus’s frequent, often inadvertent use of “i’m dead serious!” becomes the butt of many of sirius’s jokes. remus learns to use the phrase sparingly, but it still pops out unawares from time to time as remus scolds sirius in an angry or emotional state. fond as he is of padfoot, remus tries to dissuade sirius from his constant puns, but the amusingly annoying habit sticks.
nearly twenty years later, remus lupin finds himself back in hogwarts, not for class but for battle, not for learning or teaching but for spells roared in anger and fear, wand slashing violently, nearly a blur. lights flash, almost blinding him, and as remus falls, wand clattering down the stone corridor, he remembers one day many years ago filled with warmth and laughter and wordplay. smiling ever so slightly, remus lupin murmurs for the last time, “i’m dead, sirius”–and thus professor lupin’s last words are a shared joke, a fond memory, and an ironic twist of fate.