My own thoughts was going towards this. I was thinking it could be the result of poor diet in the gut. And like Psyche said if you begin to constipate the gas in your system can build up over time.Well, although it is strange, it may not necessarily be 'paranormal'. Check out this post that Psyche made on the subject:
It might be more of a health issue than anything paranormal, but I think it's still hard to say at this point.
But I find it odd that only the body durns and every thing else can remain intact. Even in some instance's the clothe's wont even catch fire, how can you explain that? Is it possible for a machine to catch fire or completely explode and burst into flames and everything else remains safe?
I am not saying this is paranormal, but I am saying that this could very well be a very unique experience taking place in someones body. It could be health issue but also a issue that might have some paranormal qualities. In other words it could be a mind, body and spirit issue all in one. But this is pure speculation