No, shallow cams are not cams that look at themselves in the mirror, but cams placed in cracks that will not accept the full width of the cam. The narrowness and shallow depth of the crack mean that 25% of the cam will not fit, or even 50%, which to an untrained eye may result in either a cam being seen as being unplaceable, or placed in a dangerously weak ordination.
With a little thought about the cam it is often possible to set a 100% secure cam in a crack that only takes 75% of the width of the cam, and in some cases a 100% unit where it seems half the cam is hanging out of the crack!
The most important thing to remember is that a cam has two ordinations, a wide ordination and a narrow one, and that if a cam is unstable and weak one way, may be solid if you flip it over (this is most noticeable in a Tricam or 3CU). Imagine a cam working like a triangle, with the force coming from the outside cams being the base, and the two central cams the point. Very often a shallow crack in a corner will have a broad face on one side and a shallow one on the other. Place the cam with the wide cams on the broad face and the central cams touching the shallow side. If the crack is very shallow you may find that one of the central cams is not touching at all. don’t be alarmed, it may not be 100% but the strength of 3 cams should still be effective (the cam is working like TCU).
The Totem has another advantage in that it can clipped off onto two cams which although not as strong as 3 or 4, could still be effective.