A mortician wrote the following:
“The majority of people who come into our home have at least one open-casket viewing, even for those who choose cremation. This can present a problem because of the staggering number of very violent ways you can die. We had a homicide victim who had been stabbed over a dozen times
and then set on fire. We’ve had a depressing number of people with self-inflicted gunshot wounds to the head and chest. I’ve even dealt with a decapitation. And, with very few exceptions, they’ve all had open caskets.
Restoration is as much an art form as it is a science, and with a good mortician, there's very little that can't be fixed. We have a wide range of tools at our disposal, depending on what needs to be done. Some of the stuff is pretty basic, like covering bruises and cuts with wax and cosmetics. If the person had heavy injuries to their head, we can rebuild large portions of their skull using a special type of putty, wax, or plaster of Paris. We can reattach severed limbs using special materials to rebuild the damaged bone and muscle.
So for instance, to fix a decapitation, you use a wooden dowel to rejoin the head and body, then suture the neck back together. With a little wax and cosmetics, they can even wear a normal shirt or dress.”
https://www.cracked.com/personal-experiences-1368-5-horrifying-truths-about-funeral-homes-from-undertaker.html