What can cause rectal bleeding?

Lots of stuff: Hemerrhoids, cancer, trauma, diverticulosis, ulcers, meckels diverticulum, a-v malformation, infection and more. I once had a "vampire" who presented to the er with blood in his stools from drinking blood from the hospital blood bank.

Many possibilities: Hemorrhoid, anal fissure, anal fistula, draining peri-rectal abscess, colitis, colon polyps, bleeding stomach ulcers, bleeding colon diverticula, colon vascular malformation, colon or rectal cancer, and maybe others.