Chicken liver, Beef liver, Cod liver oil (was anyone else tortured with the stuff as children) ... it is all the same. When I was a kid, my parents decided that liver should be a regular part of our weekly dinner rotation-- they said it was for "iron", but I think it was some sort of character building thing to teach us that life isn't all good things (like steak and bacon).
Let me say something about cod liver oil. Whenever any of us kids complained about being sick, my mother would reach for the wretched stuff. Strangely it worked... we never complained about being sick-- we were the healthiest kids around (we may be the only kids who did tricks to lower the reading on a thermometer).
Snails are fine as food. Tongue and tripe are perfectly acceptable (and delicious when prepared well).
Liver's sole purpose is to filter poisons from a body so that they can be eliminated.