Place short side of cake toward you. Poke toothpick in cake at a point 4 inches from top and 1 inch from outside edge, on both sides. Poke toothpick in cake at bottom, 1 inch from outside edge, on both sides. Cut 1x8-inch piece (marked with toothpicks) from outer edge of each side. Cut each piece in half crosswise, forming 4 (1x4-inch) pieces. Cut neck hole from top of cake.