If you see blood in your shit then it could be a sign of serious problems. Red blood in the shit means the shit is in contact with the blood in the anus, colon, or the lower part of your digestive system. Black blood in the shit means that you are bleeding in the upper part of your GI, specifically in your stomach, duodenum, or small intestine.
If the bloody shit is black then there is a chance that it is very smelly. It smells like fish that were left on your counter top for weeks. It smells so bad that you could vomit just by entering the room with some black shit.
Why do you have black bloody shit? It could be you have an ulcer in your stomach from too much alcohol or taking too much Advil or Motrin. Black bloody shit is an emergency and you must seek help.
Red bloody shit could mean you have a hemorrhoid or something is bleeding in the anus or sigmoid colon, like a tumor, polyps, fistula etc. You need to see a doctor so he can examine your shit.