Marshmallow ingredients include sugar, corn syrup, modified corn starch, dextrose, gelatin, water, tetrasodium pyrophosphate, artificial flavors and artificial colors, which means that there are no horse hooves as part of the recipe. Due to the presence of gelatin, an animal byproduct, there is a rumor that horse hooves are an ingredient as part of anything that contains gelatin. However, actual horse hooves are not made into gelatin.
Gelatin is a thickener used to make many desserts and savory dishes, including nougat, Bavarian cream and aspic. Gelatin is made from pig skin and bones, although other animals, such as sturgeons, are used for kosher purposes.