It was the ghost of a small dog- some sort of terrier possibly. It was shadowy. It came through a closed door and disappeared under our table. It did it more than once which shows it's running on a loop- as most hauntings do. There's no consciousness there; it's simply a recording of something that happened once and got fixed in the ether because it was connected to strong emotion.
I won't tell you the name of the pub or its location because people can be funny about such things. Some establishments are happy to trade on their ghosts while others would prefer to keep quiet about them.
Ailz mentioned the dog to the barman and he replied, noncomittally, that they'd been told they had a ghost. They probably have several. A lot goes on in a pub, a lot of emotion gets expended. There will have been fights, trysts, births, deaths, murders even. Most pubs are haunted- even modern ones.