Lunchen Down is a native Scottish dish, traditionally eaten in the lowlands, consisting of wool soaked in lambs fat and gravy, which is usually eaten with stewed lamb and cabbage. It is believed to be a natural colon cleanser as the wool is expected to clean the digestive tract on the way out.
A girl is eating her lunch (or any meal really) and she is shitting it out while you eat the shit. If you please, you may also regurgitate the shit into her mouth and she eats it, shits it out, and the process continues.