You can filter multiple tags by having semi-colon between them (I think, it could be comma), and you can use + or - to indicate if the tag exists or not. However, that is effectively just providing AND functionality - there is no OR parameter option. To do your OR you will need to do mulitiple Get Next Item quereis for each OR condition - so look for Cats first and if none exists look for Dogs. The only issue with this is you will loose the prioirity/fist in first out sequence of all Cats and Dogs items - you will end up getting newer cats before older dogs.....
