Its probably trapped gases do to either a urate or chunk of poo the snake for whatever reason couldnt release... I usually just apply gentle pressure near the tail to "force" out the blockage (if you do it right you wont need excessive force, just a little extra "umph" the snake cant muster)
After this the snake generally gets rid of the rest of the gases itself.
If you aren't comfortable doing this yourself, I'd have a a herp vet take a look at the snake.