There's DNA testing for rectal and colon cancers from cells taken from fecal samples. Read all about it here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4606173/
Yes. No DNA there unless the person is bleeding or wounded inside.
But D&D is right they could probably find DNA from food you ate that havet really been digested. meat, veggies, bread, etc.
This post was edited by JakobA the unAmerican. at July 6, 2017 9:31 PM MDT
Intestinal tissue is always sloughing off cells, complete with DNA. Problem is with DNA testing that there's tons of other non-human cells being expelled along with those cells (think probiotics). That usually makes differentiating between the different cell types difficult unless specific markers can be isolated, which is the case with the occult stool DNA testing for various colon and rectal cancers. Better go back to class and review that lesson!
This post was edited by Salt and Red Pepper at July 6, 2017 9:31 PM MDT