When I am just a student in the class and someone accidentally lets a noisy one out I giggle and laugh and look in the direction of the lethal missile. Now that I do a lot of teaching and am not the student that often, when someone in my class accidentally lets one out, then I have to swallow my laughter and giggle and not even look in the direction of the explosion. I remember one time, that this guy kept cutting his chakra cheese fairly audibly and we couldn’t all ignore it if we tried and he had to say “ Sorry, Excuse me” a few times. 
In order to prevent this (nothing horrifies students more when this happens….particularly when the studio is really quiet) I have the music at a fairly audible decibel. If you are hard of hearing then you might have some trouble hearing me though. Also, when I can I urge students to avoid a heavy meal like lasagna with cheesecake immediately before class I do so. I think it’s the most embarrassing when it is a guy doing this in a roomful of attractive young women. Maybe this is why guys don’t come to yoga as often.
Also, there are certain poses that will make this happen more often than not. Boat pose is particularly lethal so I make sure the music is pretty loud in this pose. I think boat pose, particularly when it is a partner pose, is usually the evil culprit. Also, appropriately titled, “Wind – Relieving Pose” sometimes makes this happen. I guess you are pressing on the descending colon in this pose
As a teacher or student, what are your experiences of observing this in a class? How did you react?