And so you drag yourself through the aisles, listless, a little anxious, wondering how to choose. Finally -- almost closing time -- you spot something in the "Classics" section: A NIGHT AT THE OPERA, a Marx Brothers standby. Gratefully you snatch the empty box and take it up to be filled. You're smiling, ready to be satiated, ready to numb your mind. But then the counterman tells you. . .