he put sealing wax in the earpieces of my stethoscope ; he mixed dried feces in my tooth powder ; and , in one memorably unfortunate incident , right before i was to take my final exams before the entire governing board of the society , he laced my tea with an extract of dried beans heavy in oligosaccharides , a sugar that most human beings-including me- can not digest , causing excessive bloating and , at least in my case , explosive gas .