Bus Etiquette question

What, exactly, is the correct response to take when you’re on the bus with a phantom farter?

I was on a very full #4 on the way home the other evening, and for most of the trip, at regular intervals, the overwhelming pong of a bottom-burp would waft its way through the throng.

Of course, if one is of a guilty disposition like myself, you assume that everyone else assumes that you were the guilty party.

How does one comport oneself as to make it patently obvious that the culprit is not, in fact, one’s own bottom?