1) Be interested enough in the reflection to watch it long enough to see the spot
2) Be observant enough to notice the spot
3) Be curious enough to care about the spot
4) Understand that the animal in the mirror is itself
5) Collapse the logical chain that: (a) if the animal in the mirror has a spot, and (b) the animal in the mirror is itself, then therefore (c) it has a spot.
6) Think to use the mirror as a tool for investigation.
An animal could plausibly get (4) without getting enough of the other steps to actually start investigating. To me, (5) seems like the most difficult leap of intelligence of all of these, and it doesn't really have to do with self-awareness-- it's more about complex inference and logical reasoning. (6) also suggests that the capability for tool use might be a prerequisite.
Most cat owners understand (including other posters in this thread) that cats know the difference between their own reflection and another real cat seen through a window. Disinterest is one explanation (though that doesn't happen with actual cats in a window), but I don't think cats' failure in the "spot" experiment is enough to exclude that they are indeed capable of (4).
On top of that, I don't think this experiment says anything at all about the nature or presence of "consciousness".