Unless it's when you're resting on the sofa, reading a book, with your dog sleeping beside you, when he suddenly jumps up and starts barking at something ... but there wasn't a noise, and everything seems fine around the house. So he lies down and goes back to sleep, but you're now paranoid and keep scoping out the room, waiting for something to happen that would explain his reaction. But probably not ghosts.
However, cats in particular think it's hilarious to freak you out by suddenly jumping up, staring into the darkest corner of the room and hissing as though there's something there you can't see - so you can end up thinking there really are ghosts.
Little kids do it too. My son used to point at the ceiling and ask me why there were cats up there. We didn't have cats and last time I checked they don't fly. Creeped me out.
@Blindbird Your son sounds like an absolute genius - I'd bet money on him being a respected author one day if he can come up with stuff like that!
@Jnei genius/whack job, could go either way.
@Blindbird Aren't they the same thing?
Looks Like I got the double points this time dude.