Various animals demonstrating a sort of crypsis called masquerade. This is where, instead of predators and prey just not noticing a thing, they notice it and don’t give a fuck because they don’t think it’s food.
Which is one of those things where we’re kind of getting into what the definition of is is, because we can’t exactly sit down and talk to animals and go “Hey, did you see that rock over there?” “Yeah, it’s a rock. So what?” “It’s really a stonefish.” “Oh, shit son.”
Above: A stonefish.
This also only really works if the animals they’re trying not to be noticed by know what “a rock” or “a leaf” is and know that it’s not good to eat. It’s further confused by the fact that a lot of the known examples also provide the benefit of crypsis, where if they’re lucky an animal won’t get noticed at all because they’re just blending right into the rest of the reef or tree or leaf. (A notable exception is the bird-dropping caterpillars, whose coloration and patterns stand out pretty clearly and brightly against most backgrounds.
Given how much a lot of these masquerading bugs look like leaves, they’re probably also contributing to a large number of the “herbivore with occasionally- or incidentally-taken insect” entries in “diet” for animal descriptions.