They use the peritoneal lining. This is a delicate tissue, and it is prone to cancer - when it does get cancer it’s very nasty as well. It’s usually within the body, lubricated very well and thus things in contact with it will glide rather like your tongue and the inside of your cheek (but more so.) this is not a tissue that’s ever supposed to be exposed to the outer world and it’s being exposed, exposed to air, to vast amounts of bacteria, and mechanical stress constantly. All that will result in changes to the tissue. Imagine your eyelids or cheek being turned inside out, it’d undergo changes, harden, proliferate and be very unhappy. I guess the best example I can think of is something like Barrett’s oesophagus. I suspect they are going to have a lot of abnormal cell changes in them.