So here are Jenn's questions, and my answers. Keep in mind that different morticians do things differently, so my answers might not be true to what your local funeral professional does.
1. Do the bodies ever move or twitch or make noise (groans, etc.)? Yes and no. When someone dies there is no twitching or moving of the limbs and what have you. They might move a little because their muscles have completely relaxed (eyelids open, mouth opens, arms relax, etc.), but there are no other motions made by them. They can, however, make noise, usually because of air trapped in their lungs that releases, especially when we move them from their place of death onto a gurney. The air will kind of just come out, sounding like a heavy sigh. The first time that happened to me I took the guy's pulse to make sure he was dead. He was.
2. Do you really put a plug in the rectum to stop "leakage"? Yes, sometimes. The plug is actually called an A/V plug (anal/vaginal), and looks like this:
3. Do you really sew the eyes closed and/or wire the jaw closed? Kinda. With the eyes I use things called eye caps, which look like contact lenses made out of plastic, with tiny raised spots on them to "hold" the eyelid down, shown here:
As for the mouth, the other embalmers I work with wire the jaw shut using things called injector needles, wires with a little barb on the end that embeds into the gum tissue, one on the top and one on the bottom, and intertwine those two together, closing the mouth. I don't like the barbs though, they seem mean, even if they are easy, so I sew the jaw shut (my husband thinks it's crazy that I don't have any issues sewing a mouth shut but won't use a needle injector (the instrument used to force the barbs into the gums)). I might have to work on a diagram to explain how I sew it, I guarantee it isn't the way you are thinking it is done. Maybe I'll work on that this weekend, or see if I have a book with an illustration of it.
4. Do the muscles relax when you pass and you poo and pee? Yes, but most of the time that is taken care of during embalming. Not only do a lot of the people that die have on some sort of adult diaper, but they are also on diets that consist of water and IV nutrients, so they don't have much to excrete (gross) anyway. And one of the things I do during (after) embalming is called aspirating, in which i take a trocar (a long "needle" of sorts, about two feet long) and puncture the stomach and suck out anything trapped in the organs (poo, pee, blood, bile, etc) and drain it, and put in extra strong formaldehyde to embalm those organs well.
So, let me know what else you have...