I think it was on the FT forums that some-one pointed out the lack of ghost stories involving cows for example
I first heard this on QI several years ago when they were scoffing about the idea of ghosts. Someone asked why they're never of animals like cows and earth worms. No one pointed out that ghostly animals are commonly reported - dogs, cats, horses... But one of the other comics not unreasonably asked "how would you know?.. If you saw a ghost of a cow in a field its not like it would be wearing a victorian top hat". Or maybe i just imagined they said that because they should have done. At any rate their light protest was silenced by Stephen Fry sneering about how you'd notice a cow or pig in your living room. (implication being that your habitat would have once been fields and therefore animals would have occupied the space..so their ghosts should be there too).
The mockery being more important than knowledge, the "discussion" seemed devoid of any rational argument. But i've read the "why are ghosts never animals" argument used a number of times since, like a triumphant game-changer. The failings of it, it strikes me are...
1) As I said ghostly animals are reported, and widely. Even if you'd never heard of read the literature on actual apparitions you'd be culturally aware of the idea of ghostly horsemen or horse and carriages
2) How WOULD you know if an animal was an apparition? If it doesn't walk through a wall or do something extraordinary in a place it should or could not be (side note - ABCS? Lake Monsters? hairy hominids?) then why would the idea of it being a ghost ever cross anyone's mind? Again, as an aside, how can we be sure none of the people we pass in a crowded city street are apparitions? The only sincere response to "have you ever seen a ghost?" is either "yes" or "i don't know"!
3) And this is the most significant point, I think. The unspoken and idiotic implication was that everything that dies is meant to turn into a ghost. That's never been believed by anyone or any culture anywhere. That we all end up as ghosts. If it doesn't apply to humans why on earth would it apply to animals? The popular "spirit of the dead" hypothesis for human apparitions generally interprets their presence to unfinished business or attempts to communicate with the still living, typically loved ones. How would either of those scenarios apply to a lemur, a dinosaur or a fruitfly? A beloved pet on the other hand can easily be imagined to have those motivations for appearing to a human after death, if such things are possible. And what do you know, apparently some of them appear to do just that. Bessie the sheep on the other hand has no message to convey.