They never smell and are always silent.
As a matter of fact, I've farted at least 20 times since I've been here in your office.
You didn't know I was farting because they don't smell and are silent.
The doctor says, "I see. Here's a prescription. Take these pills 3 times a day for seven days and come back to see me next week."
The next week the lady goes back.
"Doctor," she says, "I don't know what the hell you gave me, but now my farts ... although still silent... stink terribly." The doctor says, "Good! Now that we've cleared up your sinuses, let's start working on your hearing."