Lay the sausage flat on the cutting board and cut one end lengthwise up to the middle. Rotate 90 degrees and cut again. This will make 4 legs. You can stop here or cut each leg into half to make 8 legs.
Heat the oil in a small skillet over medium heat. Cook and stir the sausages for 5 minutes.
If using, add the ketchup before turning off the heat.