Hot take: I just learned from a museum plaque that the first auto body filler was basically horse manure and glue.
I was at the transportation museum in Detroit and read that in the 1920s, they'd mix glue with stuff like ground-up horse hooves and wood fibers to fill dents before paint, which is wild compared to the Bondo we use now.
Remember reading that too and it always gets simplified. The "horse manure" part is mostly a myth, it was usually just ground hooves and hide glue. Still pretty gross by today's standards, but not quite that literal.
But didn't they use actual horse hooves in the glue itself though? I mean, even if it wasn't straight up manure, it's still crushed up parts of a horse's foot holding your fake nails on. Just trying to figure out if we're splitting hairs over what "hoof" means in this context.