People who've known me for a while know that I don't eat mammal tissue. I used to say
red meat instead of
mammal tissue but I got tired of repeatedly dealing with my mother's thinking that, because the pork industry was calling pork
the other white meat, it somehow was no longer red meat.
In fact, I especially don't want to eat pork, because my more general rule is Never eat anything that could have loved you. and I'm quite sure that a pig could have loved me. Indeed, I think that various non-mammals, such as crows and parrots, are capable of things such as love.
An Internet friend recently mistook my standard for a reciprocity rule, as if I would reward various creatures on the chance that they might love me. But it's really a capacity rule; I don't want to eat an animal who has enough psychological sophistication for love.
I am willing to eat other animals. I'm even willing to eat animals whose ancestors could have loved me, but who, as a result of how they have been bred over many generations, now seem to lack such capacities. (However, I am put uncomfortably in mind of Lovecraft's story,
The Rats in the Walls, in which human beings had been bred by cannibals to a much diminished intellectual state.)
As a result of my desire to avoid consuming creatures that are somewhat conscious, and of my special concern for pigs, I find myself thwarted when it comes to foods that contain gelatin, including marshmallows. It is possible to derive gelatin from fish, or to substitute for gelatin various non-animal products (such as agar-agar) in the making of things such as marshmallows. But, for the most part, gelatin is derived from the skin of pigs and substitutes for gelatin are not used.
Kosher gelatin proves to be a trickier matter than one might imagine. Partly that's because gelatin can be made from bits of cow (still not on my diet). But, also, there's a Rabbi Dovid Cohen who argues, perhaps with sincerity, that bones and skin are considered inedible under Judaïc Law, and that therefore a manufacturer has a sort of clean slate when beginning with them. OU kosher certification doesn't entail a promise that pig tissue did not go into any gelatin that might be present.