1. Bring a large pot of water to a boil. Add the sausages and cook for 5 minutes. Remove the sausages with tong and drain on paper towels.
2. In a large skillet, heat the oil over medium-high heat. Fry the sausages until evenly browned, using tongs to turn. (A fork would pierce the casing, allowing the juices to escape and dry the meat.) Drain on paper towels for 5 minutes.
3. Cut the sausages into 1 1/2-inch lengths. Serve on cocktail toothpicks with the mustards for dipping.