1. Place the hog's head in a large pot and cover with water. Bring to a boil, then reduce heat and simmer for 3-4 hours until the meat is tender and falling off the bone.
2. Remove the hog's head from the pot and let it cool. Strain the broth and set aside.
3. Once the head is cool enough to handle, pick off all the meat, including the skin and fat, and chop it finely.
4. In a large mixing bowl, combine the chopped meat with onions, celery, bell peppers, garlic, salt, black pepper, red pepper flakes, and cayenne pepper.
5. Gradually add the reserved broth to the meat mixture until it reaches a thick, spreadable consistency.
6. Line a loaf pan with plastic wrap and pour the mixture into the pan. Press down firmly and cover with more plastic wrap.
7. Refrigerate for at least 4 hours or until set. Slice and serve cold.