As a minor clue, though, allow me to introduce you to a wonderful word that I found a few weeks ago whilst idly thumbing through our copy of Mr Chambers' fine dictionary.
The word is "curmurring" which is a noun (there is no verb "to curmur", although there really should be).
A curmurring is a rumbling sound made in the bowels, especially when caused by the imminence of flatulence.
So - it's the griping noises just before you let one go.
I'd have to guess that this fellow has been beset by considerable curmurring prior to his much needed release.
photo from: thebeatbreakfastcrew.blogspot.com
My own curmurring in the immediate past has, you'll be pleased to hear, produced astonishingly copious results in all sorts of interesting forms and from varying exit points which I won't bother you with now.
I've managed a short pootle around the lake this afternoon and eaten my first solids in about 40 hours for breakfast this morning. I'm actually not too bad at all as I write and it's back to the grindstone tomorrow for a five hour stint of trying not to laugh out loud at the public's inability to understand simple information. In return, the public will be innocently trying to infect me with something else. Ho hum.