Peter goes to the doctor and says, 'Doctor I have this problem with gas, but it really doesn't bother me too much. They never smell and are always silent. As a matter of fact I've farted at least 20 times since I've been in your office. You didn't know I was farting because they didn't smell and are silent.'
The doctor says, 'I see. Take these pills and come back to see me next week.'
The next week Peter goes back. 'Doctor,' he says, 'I don't know what the hell you gave me, but now my farts, although still silent, stink terribly.'