What are your current water test results? If it's been more than a couple of days run a full set of tests now just to be sure.
They do expand and contract a lot and they do "expel" left over good after a good meal. This could simply be "bathroom time".
However, when stressed (for whatever reason) they can also expel their organs and this is NOT a good sign.
How old is the tank?
What type of lights?
How long have you had it?
The more information you give us the better equipped we will be to help. A picture can be VERY valuable here
