Horses that Wiggle When You Eat Them
Jell-O is 98% sugar and the remainder is ascorbic acid, artificial flavor and color and the hooves of Mr Ed. Most geletin in the USA is extracted in the processing of animals hooves. So, if the Jell-O were added to cake recipe it would affect the delicate balance of leavening by preactivating the soda and baking powder causing huge tunnels and a flat surface. In something as rich in fat and dense as cookies it simply adds color and a tart flavor.