Munch’s Scream cannot be critiqued for abstraction (lack of mimesis) if we consider that the natural world is not in any way defined by individual visual perception. Visual perception is, instead, one way of perceiving whatever composes the natural world (i.e. light reflected back into rods and cones).
We could say that the artistic abstraction of Scream’s environment is actually a method of mimicking what we recognize as abstract in our own experience; for instance, emotional turmoil or existential angst. It would be reasonable to see Scream as nothing less than imitation, if the subject is abstracted by its own nature. Which would, in turn, bring us back to Scream as an imitation of the natural world as we perceive it as individuals, but in a non-visual way.
With some imagination, Scream can easily be seen as imitation of the visual experience of the natural world, with no stylistic liberties on perception, but from the point of view of a pet dog. Perhaps this is how an animal, with less developed facial recognition, would see a human, as an infant scrutinizing an adult. Poor eyesight smears larger portions of the landscape into simplified patterns. The thick swirls are HD smells interpreted in visual terms. The colors might correlate to a canine’s spectrum.