Animal manifestations... 
Source: http://www.ourcuriousworld.com/TypesofGhosts.htm
The question of whether an animal—usually a family pet—might be capable of manifesting itself is a source for considerable debate. As we discussed earlier and the case for immortality, it appear that animals do not possess the prerequisite sentience necessary to be considered a conscious personality, so it is hard to understand how their 'essence' might survive death and be capable of manifesting in the physical realm. However, numerous anecdotal accounts and a few examples caught on film suggest otherwise, so we must take this possibility into account as well.
But if animals lack a personality or the type of consciousness that makes such a thing possible, what is happening here? Do animals, in fact, possess more of what we would define as a soul than we imagine, or is there some other explanation available to explain this discrepancy?
A couple of possibilities present themselves. First, since many people frequently form a very strong bond with their pets, it's not remarkable then when ghosts of those pets sometimes enter into the mix. The question, however, is not whether these manifestations are being produced by the conscious, free-will actions of the deceased pet—as it is assumed human based ghosts or personalities do—but if they are produced subconsciously by the viewer.
This is not to imply such encounters are hallucinations-though this may sometimes be the case-but that the human mind might hold the image of the beloved pet so tightly in its subconscious that it might be able to inadvertently manifest it under ideal conditions. The apparition, then, is not the literal spirit of the dead animal, but a type of 'memory bubble' produced by the observer's own inherent but unconscious telekinetic energy. In this case, it is the owner's love for their pet that keeps the pet's spirit alive, not the inherent nature of the animal itself. The fact that the vast majority of animal ghosts are those of beloved family pets-manifestations of regular farm animals and wild animals are far less common-could be an important clue that this might be the case.
Another possibility is that animals do possess some very basic consciousness and may attach themselves to physical places in the same way some humans do; the manifestations, then, may be temporary residual energy bursts unconsciously created by even the most primitive animal consciousness for a brief period of time, and one that lasts only until the basic energy of the creature fades and it eventually winks out of existence. The analogy would be that of a glowing ember that continues to glow for a time after the fire has gone out; the animal's consciousness may initially survive physical death for a time before eventually dissipating into nothingness or, perhaps, being absorbed into some form of greater 'animal consciousness'.
On the other hand, since most animal manifestations are of higher order animals such as dogs, cats, and horses, it's entirely possible that even low-levels of consciousness—that state of awareness just below full sentience—might actually be capable of surviving death just as a human's may. The fact that manifestations of more primitive animals such as reptiles, amphibians, fish, and birds are almost unheard of also strongly suggests such a possibility. Of course, this is all purely speculative, but then the intricacies of consciousness and just were one might draw the line between sentience and non-sentience is not always easily defined.
As such, while I personally find it hard to imagine how an animal's consciousness—even that of a more advanced one—could survive death, the possibility that it might has to be at least considered.
Image source:http://www.worth1000.com
Source: http://www.ourcuriousworld.com/TypesofGhosts.htm