He could be bleeding through the rectum but he could also have blood in the colon
or nearby areas instead. 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.