1) benign result from recent diet. When one does an occult stool sample, which tests for blood in stool, there are dietary restrictions for three days before; like beets, spinach, canteloupe, red meat, horse radish, iron supps.vit. D, aspirin and NSAIDS,and some others I can’t remember…
2) Serious issue of blood in stool (intestinal bleeding). If it happens more than a day or so, have yr “friend”” see a Dr.
3) Google occult stool tests for reliable info (Mayo clinic, ect.) There are now apparently tests available from pharmacy rather than a Dr. Dr’s kit that requires some nose-holding poking around in toilet w. a clean wooden stick…or if you have two-yr old at home, he might enjoy doing it.