ROSSIE PRIORY STONE The art itself actually predates Christianity, and some of its symbolism is obscure. The continuous interlace represents eternity, while the depiction of the hunt, astronomy, angel and beasts are suggestive of the Druidic nature of the old religion.		Until the arrival of Christianity even vegetation was tabooed as a motif in Pictish ornament, hence there was a concentration upon geometry and mathematics, and abstractions which were not copies of created life. This was, and is, a feature common to many religions around the world.
This is a page from Celtic Art : the Methods of Construction by George Bain.

These are Brythonic fighting dogs as portrayed in the Book of Kells. The Celts are believed to have introduced large, mastiff-type dogs to Britain around 400 BC. Not particularly fast but very strong, they were also used for hunting wild boar. The Romans took many of them for use in the arena, where it is said they could snap a bull's neck with one strike. They may have been ancestors of the famous "Irish" hounds of the Middle Ages, which stood over four foot high at the shoulder and are recorded as being a sandy colour with a shape similar to the present wolfhounds, but much bigger. If the Celtic dogs, though slower, were even more powerful, then they must have been truly fearsome opponents in battle.