The maggot-covered head found by Gary the caretaker is actually the head of the director, Christian Viel.
As with the Wes Craven film The Hills Have Eyes (1977), this movie is based on the legend of Sawney Beane and his family (a wife, eight sons and six daughters), a feral clan said to have inhabited and roamed the coast of Galloway, Scotland, murdering and often eating travelers and isolated residents, in the 15th or 16th century. They were eventually captured by troops of Scotland's King James, judged to be insane and executed without trial (one story says that soldiers tied them to stakes, burned them alive, then scattered their ashes in a nearby cave and sealed the entrance to the cave with huge, heavy boulders). There is still debate over whether the Beanes actually existed.
The title of the film is an Irish word for that part of the year that English speakers call Halloween. Samhain, for an English speaker, would approximate in pronunciation to "sow-in". Samhain is the part of the year when the living can contact their dead ancestors.
The scene where Shape #2 attacks Barbara after she took her shower was mostly cut out. The only thing that made it into the film was his hands grabbing her feet from under the bed.
Mark Borchardt was originally cast in the movie and his scenes were shot but not included because of local union problems in Canada.