There's a question I want to dig into a little further before I arrange another rendezvous between Hamlet and Burrhus (Frederic Skinner), a question regarding self-consciousness. This is one of innumerable capacities ascribed until recently only to humans. Various experiments with mirrors and paint have widened the circle of self-conscious creatures just a little bit, to include apes and magpies (!) among a few others, but I think the assumption that underlies the research may be too restrictive to allow a full description of the phenomenon. While it may be difficult or impossible to demonstrate under scientific controls (this is clearly a case in which observation itself may distort the nature and behavior of what we observe), informal study argues strongly for the emergence of "personality" in many social species who (pronoun used advisedly) fail the mirror test. Canis familiaris, to take one salient example.
What if one accumulates (even if unwittingly) a distinct and precious identity, an identity one is motivated to defend (even if reflexively)? Mightn't this constitute a kind of self-consciousness, whether or not the self is pinched off from consciousness and set out as an object for one's contemplation and deliberate manipulation? I think anyone who has ever observed the wounding of a dog's pride or a cat's dignity must admit the possibility.
The counterexample of the octopus also supports a more expansive definition of self-consciousness. Experiments performed using HDTV suggest that, however intelligent, an octopus has no personality: that is, it demonstrates the patterns of behavior that we generally attribute to personality, but these patterns are extremely short-lived. An octopus that is extroverted and aggressive one day may be terribly timid the next. (Wonderful that the subject of this research was Octopus tetricus: vulgarly, the "gloomy" octopus.)
If the range of an animal's behavior (and the probability of any specific response to a stimulus) were determined simply by a passive stockpiling of experience and not by any active sense of internal coherence - of individual integrity - one would not expect to see such wild variations in the robustness of behavioral patterns among species.
**There's another experiment, performed back in 2008, that hints at a canine capacity for self-consciousness. Austrian researchers trained a pair of border collies to sit and shake on cue, then measured the time it took for the behaviors to extinguish when they received no reinforcement. The salient data came from a comparison between "control" trials, wherein one of the dogs worked alone, and trials wherein the two dogs worked side by side but only one received reinforcement. Behaviors extinguished significantly more quickly in the second case (and the unrewarded dog showed many more visible signs of frustration). Discussion of the research has focused primarily on the question of whether this demonstrates that dogs have a sense of "fairness," but it certainly suggests that they have a vigorous sense of "me" distinct from "him," a protective self-regard that might amount to a form of ego.