There is a faint slash under the throat of the big one - fainter than most I have caught there, but definitely not present on the rainbows. I was also going on mouth size/shape (and teeth), spotting, fin shape and color. It is a bad angle to see the head, but the maxillary does extend past the eyeball (this is a female with small eggs present, so her mouth is smaller). It is common to catch coastal cutthroat in this lake with this coloration - they are stocked as fingerlings in the fall and I have caught 4 inchers that look the same. One noticeable difference also - once the scales are removed (and they are smaller scales on the cutthroat) the skin had no resemblance to that of the rainbows - no red rainbow stripe.