Gelatin is made from bones and hides

Sometimes the most innocuous of foodstuffs contain constituents whose origins are less than appetizing. Such is the case with JELL-O, a dessert that has graced millions of dinner tables since its 1897 debut.

The production of gelatin starts with the boiling of bones, skins, and hides of cows and pigs, a process that releases the protein-rich collagen from animal tissues. The collagen is boiled and filtered numerous times, dried, and ground to a powder. Because the collagen is processed extensively, the final product is not categorized as a meat or animal product by the federal government. Very strict vegetarians avoid gelatin entirely.

Snopes.com