In a large bowl pour hot water over margerine. Stir in powdered milk, salt and egg. Add flour 1/2 cup at a time mixing well after each addition. Knead 3 to 4 minutes, adding more flour if necessary to make a very stiff dough. Pat or roll to 1/2 inch thickness and cut into bone shapes. Place on a greased baking sheet and bake at 325 degrees for 50 minutes. Allow to cool and dry out until hard. Makes approximately 1 1/4 pounds. Costs approximately $.25 per pound.