Yes, that's right. Most plants have a number of defense mechanisms to ward off insects, bacteria, fungus, etc. to avoid being devoured. (Plus other physical bar

Yes, that's right. Most plants have a number of defense mechanisms to ward off insects, bacteria, fungus, etc. to avoid being devoured. (Plus other physical barriers, but that's not the problem here.) If a certain animal can eat a certain plant, it's usually because the animal has its own mechanisms for handling the defensive proteins, or hosts bacteria that can do it. You're probably missing some of these. Heat makes a protein unfold; and unfolded protein still has the amino acids you can metabolize, but no structure, so it can't do anything.