Having blood in the colon is bad, what can I tell you, and it can be seen when the
cat goes to the bathroom. Inflammation
in the rectum can be caused by food allergies, again, constipation, diarrhea or bacterial infection. You want to take the cat to the vet to get a diagnosis, and it might be a good idea to take a stool sample to the vet with you. Hopefully, your cat's problem is he is having a bit of a hard time evacuating.