Fish the side of the spine adjacent to deepest water, since, in normal lighting, the trout prefer immediate proximity to depths. However, during the security of a chop, they favor the shallow side as well. Often, those wily fly-fishers, who avoid movement and wear blending clothing, see their quarry take the fly. For this reason, many prefer to wade clearer lakes, whenever possible, and visually witness such exhilarating takes. If such opportunity arises for those with nerves of steel, resist setting the hook and watch the actual take for a lesson in trout behavior can be gained under such conditions.
Trout generally take the fly by way of suction, even when they strike.
Yes, they do open and close their mouth on the fly. Nevertheless, they also simultaneously inhale an amazing amount of water into their mouth and shoot it out their gills with the resulting vacuum washing the morsel in or holding it. The mouth may remain open for an instant. For this reason, we learn to slow the moment before striking. Many wait until the fish turns, which is the moment one initially senses the take in stained waters.