1. Cut the chicken and duck into one-centimeter/half-inch strips and thread the strips onto the skewers, about 50 grams/one and three-quarters ounces per skewer, leaving about four-centimeter/one and a half inches clear at the end, so it can rest it on the bottom of the pot without sticking. Arrange on a serving platter. Set platters of couscous and bowls of Tunisian relish on the table.
2. Fill a metal fondue pot one-third full with oil and add the duck fat trimmings. Heat the oil to 180 degrees Celsius/350 degrees Fahrenheit or until a cube of bread browns in 40 seconds. Very carefully transfer the pot to its tabletop burner. Remove the duck fat when it becomes brown.
3. Invite guests to cook the skewers of duck and chicken in the hot oil for two minutes, then eat with the couscous and relish.