I didn't need to stick my gramp's chickens through the roof of their mouths to loosen their feathers. We did scald in batches and had a big commercial grade picker with a horozonal drum with rubber "fingers" that did all the plucking. What you are talking about is not used for killing but to help release feathers without burning all of that shoo-nasty-nasty fossil fuel needed to scald 1,000s of chickens per hour. You can do it at home and by hand pretty good with a little practice or if you have a mechanized killing line like the big prossers do, a computerized thingamajiggy works well. Because avian brains are sorta primitive when they are killed quickly volintary brain and mussle activity continues for a spell. Think of it like a snake with its head chopped off that keeps moving till Sundown and cooler temperatures halt movement. A small keen pocket knife pen blade is the best to use in my opinion.