Hello, firstly thanks for listening! My partner and I got a new dog just before Christmas who had been cat tested and was apparently un-bothered by cats. This was important to us as we have two fairly nervous cats who are about 6 years old, we have had them for 5 years. He is a Spanish street dog so we don't know much about his makeup - at a guess could be a blend of terrier, Portuguese podengo, possibly pyrenean shepherd, no doubt a bunch of others too. He is around 18 months old, 11.5kg. In his first week, he really wasn't fussed about the cats, looked away, left them alone, walked away from them, etc. We were super thrilled, and the cats began to get braver and walk through the room past him. Then after about a week he began to move towards them and bark - now if he sees them he will leap up and bark at them, which of course means they run, then he runs, which is a great game. The cats have grown even more terrified, they are pretty skittish and have more or less retreated back upstairs. They rarely try to get past the dog now if we are in (unfortunately we have a house that is linear and prohibits any exit that doesn't involve walking past the dog). We have researched predatory chasing but I'm not sure that's what it is, because he does respond when we call him off. He also chases squirrels in the park, he has chased a fox at dusk, and a random cat we saw in a field. On none of these occasions has he barked, but has got into that 'focused' state where he cannot be called back. On the whole he is quite well behaved, with good recall - apart from in these outside chase scenarios. He is social with other dogs and loves to play chase in the park, again with no barking (and often seems confused if the other dog barks). So I'm a bit confused as to what it is with the cats. Could it be territorial? Herding? It doesn't seem aggressive because he's never tried to hurt them, and on more than one occasion has been close enough to do serious harm if he wanted. There's no growling either, and he is always in a state of high excitement after (whirling waggy tail, pricked forward puppy ears). In the last day or two I've had some success in distracting him with treats when one of the cats was nearby and he began to stare at her. We are starting obedience training in February, he does have most of the basics but it's good to consolidate, plus a nice bonding experience. Hopefully being more consistently attentive to our commands will help. We also try to make sure he gets a good, tiring walk in the morning (lots of running around with other dogs!) so he's not looking to play or too bouncy in the house. Anyone have any insight or thoughts? Thanks!